diff --git a/doc/qbk/0.main.qbk b/doc/qbk/0.main.qbk
index c26b99b1..71fbc454 100644
--- a/doc/qbk/0.main.qbk
+++ b/doc/qbk/0.main.qbk
@@ -53,7 +53,7 @@
 [def __result__                 [link url.ref.boost__urls__result `result`]]
 [def __static_pool__            [link url.ref.boost__urls__static_pool `static_pool`]]
 [def __static_url__             [link url.ref.boost__urls__static_url `static_url`]]
-[def __string_value__           [link url.ref.boost__urls__string_value `string_value`]]
+[def __const_string__           [link url.ref.boost__urls__const_string `const_string`]]
 [def __string_view__            [link url.ref.boost__urls__string_view `string_view`]]
 [def __url__                    [link url.ref.boost__urls__url `url`]]
 [def __url_view__               [link url.ref.boost__urls__url_view `url_view`]]
diff --git a/doc/qbk/1.1.quicklook.qbk b/doc/qbk/1.1.quicklook.qbk
index e86b86ea..e1dcf960 100644
--- a/doc/qbk/1.1.quicklook.qbk
+++ b/doc/qbk/1.1.quicklook.qbk
@@ -69,7 +69,7 @@ call the same function without the word encoded:
 ```
 ]]]
 
-The function `query` returns a __string_value__, which is a library type
+The function `query` returns a __const_string__, which is a library type
 that models a read-only string with ownership of the underlying buffer,
 which uses a type-erased allocator. All functions which return string
 values accept an optional __Allocator__ parameter when when omitted,
diff --git a/doc/qbk/quickref.xml b/doc/qbk/quickref.xml
index 274865d2..c2782d47 100644
--- a/doc/qbk/quickref.xml
+++ b/doc/qbk/quickref.xml
@@ -73,7 +73,7 @@
           <member><link linkend="url.ref.boost__urls__error_code">error_code</link></member>
           <member><link linkend="url.ref.boost__urls__error_condition">error_condition</link></member>
           <member><link linkend="url.ref.boost__urls__result">result</link></member>
-          <member><link linkend="url.ref.boost__urls__string_value">string_value</link></member>
+          <member><link linkend="url.ref.boost__urls__const_string">const_string</link></member>
           <member><link linkend="url.ref.boost__urls__string_view">string_view</link></member>
           <member><link linkend="url.ref.boost__urls__system_error">system_error</link></member>
         </simplelist>
diff --git a/include/boost/url/authority_view.hpp b/include/boost/url/authority_view.hpp
index ad4514d3..a87b6b4d 100644
--- a/include/boost/url/authority_view.hpp
+++ b/include/boost/url/authority_view.hpp
@@ -522,7 +522,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -536,7 +536,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     userinfo(
         Allocator const& a = {}) const
     {
@@ -614,7 +614,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -630,7 +630,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     user(
         Allocator const& a = {}) const
     {
@@ -730,7 +730,7 @@ public:
         allocator is used, and the return type of
         the function becomes `std::string`.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -746,7 +746,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     password(
         Allocator const& a = {}) const
     {
@@ -882,7 +882,7 @@ public:
         the default allocator is used, and the return
         type of the function becomes `std::string`.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -900,7 +900,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     host(
         Allocator const& a = {}) const
     {
@@ -910,7 +910,7 @@ public:
             urls::host_type::name)
         {
             // no decoding
-            return string_value(s0, a);
+            return const_string(s0, a);
         }
         pct_decode_opts opt;
         opt.plus_to_space = false;
diff --git a/include/boost/url/const_string.hpp b/include/boost/url/const_string.hpp
new file mode 100644
index 00000000..89fe6afb
--- /dev/null
+++ b/include/boost/url/const_string.hpp
@@ -0,0 +1,164 @@
+//
+// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/CPPAlliance/url
+//
+
+#ifndef BOOST_URL_CONST_STRING_HPP
+#define BOOST_URL_CONST_STRING_HPP
+
+#include <boost/url/detail/config.hpp>
+#include <boost/url/string_view.hpp>
+#include <memory>
+#include <type_traits>
+
+namespace boost {
+namespace urls {
+
+/** A constant string with shared ownership
+
+    Objects of this type represent read-only
+    strings with ownership of the character
+    buffer.
+
+    They are reference counted to allow cheap copies.
+
+    The type is derived from `string_view`,
+    which provides compatibility with strings
+    in terms of comparisons and conversions.
+
+    However, care must be exercised; undefined
+    behavior results if the string_view
+    portion of the object is modified
+    directly, for example by calling
+    `remove_suffix` or `operator=`.
+
+    Slicing, however, is supported, as
+    copies of the `string_view` portion
+    of the object are valid and remain
+    valid for the lifetime of the original
+    object.
+*/
+class const_string : public string_view
+{
+    struct base;
+
+    base* p_ = nullptr;
+
+    template<class Allocator>
+    base*
+    construct(
+        std::size_t n,
+        Allocator const& a,
+        char*& dest);
+
+public:
+#ifdef BOOST_URL_DOCS
+    using allocator = __see_below__;
+#else
+    class allocator;
+#endif
+
+    /** Destructor
+
+        Upon destruction, ownership of the shared string is released. If
+        there are no more owners, the resources for the string are released.
+
+     */
+    inline
+    ~const_string();
+
+    /** Constructor
+
+        Default-constructed strings are empty
+
+     */
+    const_string() = default;
+
+    /** Constructor
+
+        This function creates a const_string of the specified size at the
+        destination with the a custom allocator.
+
+        This function sets the destination pointer to the new string address,
+        where the user can fill its contents while the const_string still
+        owns the buffer.
+
+        The buffer is destroyed after the last const_string that refers to it
+        is destroyed.
+
+        @tparam Allocator Allocator type
+
+        @param n Number of chars in the string `dest`
+
+        @param a Allocator to create a string in `dest`
+
+        @param dest Destination
+
+     */
+    template<class Allocator>
+    const_string(
+        std::size_t n,
+        Allocator const& a,
+        char*& dest);
+
+    /** Constructor
+
+        This function constructs a copy of a @ref const_string with the
+        specified allocator.
+
+        This function allocates a @ref const_string the specified allocator
+        and copies its contents to this new string.
+
+        @tparam Allocator Allocator type
+
+        @param s The sting to copy
+
+        @param a allocator used to create this const_string
+
+     */
+    template< class Allocator =
+        std::allocator<char> >
+    explicit
+    const_string(
+        string_view s,
+        Allocator const& a = {});
+
+    /** Copy constructor
+
+        This function constructs a copy of a const_string. As const_string
+        is read-only, this function can only copy and increment the string
+        reference counter.
+
+        @param other The string to copy
+
+     */
+    inline
+    const_string(
+        const_string const& other) noexcept;
+
+    /** Copy assignment
+
+        This function copy assigns a @ref const_string.
+
+        Objects of this type are cheap to copy.
+
+        @param other The string to copy
+
+     */
+    inline
+    const_string&
+    operator=(const_string const& other) & noexcept;
+};
+
+
+} // urls
+} // boost
+
+
+#include <boost/url/impl/const_string.hpp>
+
+#endif
diff --git a/include/boost/url/impl/string.hpp b/include/boost/url/impl/const_string.hpp
similarity index 89%
rename from include/boost/url/impl/string.hpp
rename to include/boost/url/impl/const_string.hpp
index 73efdf05..ea4155f9 100644
--- a/include/boost/url/impl/string.hpp
+++ b/include/boost/url/impl/const_string.hpp
@@ -11,19 +11,20 @@
 #define BOOST_URL_IMPL_STRING_HPP
 
 #include <boost/url/detail/over_allocator.hpp>
+#include <atomic>
 
 namespace boost {
 namespace urls {
 
-struct string_value::base
+struct const_string::base
 {
-    std::size_t refs = 1;
+    std::atomic<std::size_t> refs{1};
     virtual void destroy() noexcept = 0;
 };
 
 template<class Allocator>
 auto
-string_value::
+const_string::
 construct(
     std::size_t n,
     Allocator const& a,
@@ -75,8 +76,8 @@ construct(
     return p;
 }
 
-string_value::
-~string_value()
+const_string::
+~const_string()
 {
     if( p_ &&
         --p_->refs == 0)
@@ -84,8 +85,8 @@ string_value::
 }
 
 template<class Allocator>
-string_value::
-string_value(
+const_string::
+const_string(
     std::size_t n,
     Allocator const& a,
     char*& dest)
@@ -94,8 +95,8 @@ string_value(
 }
 
 template<class Allocator>
-string_value::
-string_value(
+const_string::
+const_string(
     string_view s,
     Allocator const& a)
 {
@@ -106,9 +107,9 @@ string_value(
         s.data(), s.size());
 }
 
-string_value::
-string_value(
-    string_value const& other) noexcept
+const_string::
+const_string(
+    const_string const& other) noexcept
     : string_view(other)
     , p_(other.p_)
 {
@@ -116,10 +117,10 @@ string_value(
         ++p_->refs;
 }
 
-string_value&
-string_value::
+const_string&
+const_string::
 operator=(
-    string_value const& other) & noexcept
+    const_string const& other) & noexcept
 {
     if( p_ &&
         --p_->refs == 0)
@@ -134,7 +135,7 @@ operator=(
 
 //------------------------------------------------
 
-class string_value::allocator
+class const_string::allocator
 {
     struct base
     {
@@ -146,7 +147,7 @@ class string_value::allocator
         }
 
         virtual
-        string_value
+        const_string
         alloc(
             std::size_t n,
             char*& dest) = 0;
@@ -214,12 +215,12 @@ public:
             {
             }
 
-            string_value
+            const_string
             alloc(
                 std::size_t n,
                 char*& dest) override
             {
-                return string_value(
+                return const_string(
                     n, a_, dest);
             }
 
@@ -235,8 +236,8 @@ public:
         p_ = ::new(al.allocate(1)) impl(al);
     }
 
-    string_value
-    make_string_value(
+    const_string
+    make_const_string(
         std::size_t n,
         char*& dest) const
     {
diff --git a/include/boost/url/impl/params.hpp b/include/boost/url/impl/params.hpp
index e731207a..e6dda15d 100644
--- a/include/boost/url/impl/params.hpp
+++ b/include/boost/url/impl/params.hpp
@@ -22,14 +22,14 @@ class params::iterator
 {
     url const* u_ = nullptr;
     std::size_t i_ = 0;
-    string_value::allocator a_;
+    const_string::allocator a_;
 
     friend class params;
 
     iterator(
         url const& u,
         std::size_t i,
-        string_value::allocator a) noexcept
+        const_string::allocator a) noexcept
         : u_(&u)
         , i_(i)
         , a_(a)
diff --git a/include/boost/url/impl/params.ipp b/include/boost/url/impl/params.ipp
index c5da68d7..523443d9 100644
--- a/include/boost/url/impl/params.ipp
+++ b/include/boost/url/impl/params.ipp
@@ -24,7 +24,7 @@ reference(
     char const* const s,
     std::size_t const nk,
     std::size_t const nv,
-    string_value::allocator a)
+    const_string::allocator a)
 {
     if(nv > 0)
     {
@@ -35,7 +35,7 @@ reference(
             s + nk + 1, nv - 1 };
         auto n = pct_decode_bytes_unchecked(ev);
         char *dest;
-        value = a.make_string_value(
+        value = a.make_const_string(
             n, dest);
         pct_decode_unchecked(
             dest, dest + n, ev);
@@ -52,7 +52,7 @@ reference(
     auto n =
         pct_decode_bytes_unchecked(ek);
     char* dest;
-    key = a.make_string_value(n, dest);
+    key = a.make_const_string(n, dest);
     pct_decode_unchecked(
         dest, dest + nk, ek);
 }
@@ -100,7 +100,7 @@ operator*() const ->
 auto
 params::
 at(string_view key) const ->
-    string_value
+    const_string
 {
     url::raw_param r;
     auto it = find(key);
@@ -122,7 +122,7 @@ at(string_view key) const ->
     auto n =
         pct_decode_bytes_unchecked(ev);
     char *dest;
-    auto s = a_.make_string_value(n, dest);
+    auto s = a_.make_const_string(n, dest);
     pct_decode_unchecked(
         dest, dest + n, ev);
     return s;
diff --git a/include/boost/url/impl/params_view.hpp b/include/boost/url/impl/params_view.hpp
index 44ae38af..fb4ca19b 100644
--- a/include/boost/url/impl/params_view.hpp
+++ b/include/boost/url/impl/params_view.hpp
@@ -24,7 +24,7 @@ class params_view::iterator
     char const* p_ = nullptr;
     std::size_t nk_ = 0;
     std::size_t nv_ = 0;
-    string_value::allocator a_;
+    const_string::allocator a_;
     bool first_ = true;
 
     friend class params_view;
@@ -33,13 +33,13 @@ class params_view::iterator
 
     iterator(
         string_view s,
-        string_value::allocator a) noexcept;
+        const_string::allocator a) noexcept;
 
     // end
     iterator(
         string_view s,
         int,
-        string_value::allocator a) noexcept;
+        const_string::allocator a) noexcept;
 
     string_view
     encoded_key() const noexcept;
diff --git a/include/boost/url/impl/params_view.ipp b/include/boost/url/impl/params_view.ipp
index 570fcb8e..b7ccaa9c 100644
--- a/include/boost/url/impl/params_view.ipp
+++ b/include/boost/url/impl/params_view.ipp
@@ -44,7 +44,7 @@ value_type(
     char const* s,
     std::size_t nk,
     std::size_t const nv,
-    string_value::allocator a)
+    const_string::allocator a)
 {
     if(nk + nv == 0)
     {
@@ -61,7 +61,7 @@ value_type(
         auto n =
             pct_decode_bytes_unchecked(ev);
         char *dest;
-        value = a.make_string_value(
+        value = a.make_const_string(
             n, dest);
         pct_decode_unchecked(
             dest, dest + n, ev);
@@ -75,7 +75,7 @@ value_type(
     auto n =
         pct_decode_bytes_unchecked(ek);
     char* dest;
-    key = a.make_string_value(n, dest);
+    key = a.make_const_string(n, dest);
     pct_decode_unchecked(
         dest, dest + nk, ek);
 }
@@ -119,7 +119,7 @@ params_view::
 iterator::
 iterator(
     string_view s,
-    string_value::allocator a) noexcept
+    const_string::allocator a) noexcept
     : end_(s.data() + s.size())
     , p_(s.data())
     , a_(a)
@@ -132,7 +132,7 @@ iterator::
 iterator(
     string_view s,
     int,
-    string_value::allocator a) noexcept
+    const_string::allocator a) noexcept
     : end_(s.data() + s.size())
     , p_(nullptr)
     , a_(a)
@@ -208,8 +208,7 @@ operator==(
 auto
 params_view::
 at(string_view key) const ->
-    string_value
-{
+    const_string {
     auto it = find(key);
     for(;;)
     {
@@ -227,7 +226,7 @@ at(string_view key) const ->
     auto n =
         pct_decode_bytes_unchecked(ev);
     char *dest;
-    auto s = a_.make_string_value(n, dest);
+    auto s = a_.make_const_string(n, dest);
     pct_decode_unchecked(
         dest, dest + n, ev);
     return s;
diff --git a/include/boost/url/impl/pct_encoding.hpp b/include/boost/url/impl/pct_encoding.hpp
index 2519cd16..e193c4ea 100644
--- a/include/boost/url/impl/pct_encoding.hpp
+++ b/include/boost/url/impl/pct_encoding.hpp
@@ -193,7 +193,7 @@ pct_decode(
 template<
     class CharSet,
     class Allocator>
-string_value
+const_string
 pct_decode_to_value(
     string_view s,
     pct_decode_opts const& opt,
@@ -205,7 +205,7 @@ pct_decode_to_value(
         grammar::is_charset<CharSet>::value);
 
     if(s.empty())
-        return string_value();
+        return const_string();
     error_code ec;
     auto const n =
         validate_pct_encoding(
@@ -214,7 +214,7 @@ pct_decode_to_value(
         detail::throw_invalid_argument(
             BOOST_CURRENT_LOCATION);
     char* dest;
-    string_value r(n, a, dest);
+    const_string r(n, a, dest);
     pct_decode_unchecked(
         dest, dest + n, s, opt);
     return r;
@@ -223,7 +223,7 @@ pct_decode_to_value(
 //------------------------------------------------
 
 template<class Allocator>
-string_value
+const_string
 pct_decode_unchecked(
     string_view s,
     pct_decode_opts const& opt,
@@ -234,7 +234,7 @@ pct_decode_unchecked(
         decoded_size =
             pct_decode_bytes_unchecked(s);
     char* dest;
-    string_value r(
+    const_string r(
         decoded_size, a, dest);
     pct_decode_unchecked(
         dest, dest + decoded_size,
@@ -408,7 +408,7 @@ pct_encode(
 template<
     class CharSet,
     class Allocator>
-string_value
+const_string
 pct_encode_to_value(
     string_view s,
     pct_encode_opts const& opt,
@@ -420,11 +420,11 @@ pct_encode_to_value(
         grammar::is_charset<CharSet>::value);
 
     if(s.empty())
-        return string_value();
+        return const_string();
     auto const n =
         pct_encode_bytes(s, opt, cs);
     char* dest;
-    string_value r(n, a, dest);
+    const_string r(n, a, dest);
     char const* end = dest + n;
     auto const n1 = pct_encode(
         dest, end, s, opt, cs);
diff --git a/include/boost/url/impl/segments.hpp b/include/boost/url/impl/segments.hpp
index 7babe538..5883b38d 100644
--- a/include/boost/url/impl/segments.hpp
+++ b/include/boost/url/impl/segments.hpp
@@ -31,14 +31,14 @@ class segments::iterator
 {
     url const* u_ = nullptr;
     std::size_t i_ = 0;
-    string_value::allocator a_;
+    const_string::allocator a_;
 
     friend class segments;
 
     iterator(
         url const& u,
         std::size_t i,
-        string_value::allocator
+        const_string::allocator
             const& a) noexcept
         : u_(&u)
         , i_(i)
@@ -47,8 +47,8 @@ class segments::iterator
     }
 
 public:
-    using value_type = string_value;
-    using reference = string_value;
+    using value_type = const_string;
+    using reference = const_string;
     using pointer = void const*;
     using difference_type = std::ptrdiff_t;
     using iterator_category =
@@ -87,7 +87,7 @@ public:
     }
 
     BOOST_URL_DECL
-    string_value
+    const_string
     operator*() const;
 
     friend
@@ -166,7 +166,7 @@ public:
             std::ptrdiff_t>(a.i_) - b.i_;
     }
 
-    string_value
+    const_string
     operator[](ptrdiff_t n) const
     {
         return *(*this + n);
@@ -272,7 +272,7 @@ assign(FwdIt first, FwdIt last) ->
 auto
 segments::
 at(std::size_t i) const ->
-    string_value
+    const_string
 {
     if(i >= size())
         detail::throw_out_of_range(
@@ -283,7 +283,7 @@ at(std::size_t i) const ->
 auto
 segments::
 front() const ->
-    string_value
+    const_string
 {
     BOOST_ASSERT(! empty());
     return (*this)[0];
@@ -292,7 +292,7 @@ front() const ->
 auto
 segments::
 back() const ->
-    string_value
+    const_string
 {
     BOOST_ASSERT(! empty());
     return (*this)[size() - 1];
diff --git a/include/boost/url/impl/segments.ipp b/include/boost/url/impl/segments.ipp
index 02968633..9286e839 100644
--- a/include/boost/url/impl/segments.ipp
+++ b/include/boost/url/impl/segments.ipp
@@ -21,7 +21,7 @@ namespace urls {
 
 //------------------------------------------------
 
-string_value
+const_string
 segments::
 iterator::
 operator*() const
@@ -41,7 +41,7 @@ operator*() const
         pct_decode_bytes_unchecked(s);
     char* dest;
     auto v =
-        a_.make_string_value(n, dest);
+        a_.make_const_string(n, dest);
     pct_decode_opts opt;
     opt.plus_to_space = false;
     pct_decode_unchecked(
@@ -59,7 +59,7 @@ auto
 segments::
 operator[](
     std::size_t i) const ->
-    string_value
+    const_string
 {
     BOOST_ASSERT(i < u_->nseg_);
     auto p0 = u_->segment(i);
@@ -76,7 +76,7 @@ operator[](
         pct_decode_bytes_unchecked(s);
     char* dest;
     auto v =
-        a_.make_string_value(n, dest);
+        a_.make_const_string(n, dest);
     pct_decode_opts opt;
     opt.plus_to_space = false;
     pct_decode_unchecked(
diff --git a/include/boost/url/impl/segments_view.hpp b/include/boost/url/impl/segments_view.hpp
index ccb7b5c8..f11f4447 100644
--- a/include/boost/url/impl/segments_view.hpp
+++ b/include/boost/url/impl/segments_view.hpp
@@ -24,7 +24,7 @@ class segments_view::
     char const* pos_ = nullptr;
     char const* next_ = nullptr;
     char const* end_ = nullptr;
-    string_value::allocator a_;
+    const_string::allocator a_;
     pct_encoded_str t_;
 
     friend segments_view;
@@ -33,7 +33,7 @@ class segments_view::
     iterator(
         string_view s,
         std::size_t nseg,
-        string_value::
+        const_string::
             allocator const& a) noexcept;
 
     // end ctor
@@ -41,13 +41,13 @@ class segments_view::
     iterator(
         string_view s,
         std::size_t nseg,
-        string_value::
+        const_string::
             allocator const& a,
         int) noexcept;
 
 public:
-    using value_type = string_value;
-    using reference = string_value;
+    using value_type = const_string;
+    using reference = const_string;
     using pointer = void const*;
     using difference_type = std::ptrdiff_t;
     using iterator_category =
@@ -66,7 +66,7 @@ public:
         iterator const&) noexcept;
 
     BOOST_URL_DECL
-    string_value
+    const_string
     operator*() const noexcept;
 
     bool
@@ -146,7 +146,7 @@ is_absolute() const noexcept
 //
 //------------------------------------------------
 
-string_value
+const_string
 segments_view::
 front() const noexcept
 {
@@ -154,7 +154,7 @@ front() const noexcept
     return *begin();
 }
 
-string_value
+const_string
 segments_view::
 back() const noexcept
 {
diff --git a/include/boost/url/impl/segments_view.ipp b/include/boost/url/impl/segments_view.ipp
index 1a52f8e0..17d27eaa 100644
--- a/include/boost/url/impl/segments_view.ipp
+++ b/include/boost/url/impl/segments_view.ipp
@@ -25,7 +25,7 @@ iterator::
 iterator(
     string_view s,
     std::size_t nseg,
-    string_value::allocator const& a) noexcept
+    const_string::allocator const& a) noexcept
     : begin_(s.data())
     , pos_(s.data())
     , next_(s.data())
@@ -54,7 +54,7 @@ iterator::
 iterator(
     string_view s,
     std::size_t nseg,
-    string_value::
+    const_string::
         allocator const& a,
     int) noexcept
     : i_(nseg)
@@ -84,13 +84,13 @@ operator=(
     iterator const&) noexcept ->
         iterator& = default;
 
-string_value
+const_string
 segments_view::
 iterator::
 operator*() const noexcept
 {
     char* dest;
-    auto s = a_.make_string_value(
+    auto s = a_.make_const_string(
         t_.decoded_size, dest);
     pct_decode_opts opt;
     opt.plus_to_space = false;
diff --git a/include/boost/url/ipv4_address.hpp b/include/boost/url/ipv4_address.hpp
index 73569e65..1bb755ce 100644
--- a/include/boost/url/ipv4_address.hpp
+++ b/include/boost/url/ipv4_address.hpp
@@ -12,7 +12,7 @@
 
 #include <boost/url/detail/config.hpp>
 #include <boost/url/error.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <boost/url/grammar/parse_tag.hpp>
 #include <array>
 #include <cstdint>
@@ -160,18 +160,18 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
     */
     template<class Allocator =
         std::allocator<char>>
-    string_value
+    const_string
     to_string(Allocator const& a = {}) const
     {
         char buf[max_str_len];
         auto const n = print_impl(buf);
         char* dest;
-        string_value s(n, a, dest);
+        const_string s(n, a, dest);
         std::memcpy(dest, buf, n);
         return s;
     }
diff --git a/include/boost/url/ipv6_address.hpp b/include/boost/url/ipv6_address.hpp
index b04fcf18..e769c16b 100644
--- a/include/boost/url/ipv6_address.hpp
+++ b/include/boost/url/ipv6_address.hpp
@@ -12,7 +12,7 @@
 
 #include <boost/url/detail/config.hpp>
 #include <boost/url/error.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <boost/url/grammar/parse_tag.hpp>
 #include <array>
 #include <cstdint>
@@ -185,7 +185,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -194,13 +194,13 @@ public:
     */
     template<class Allocator =
         std::allocator<char>>
-    string_value
+    const_string
     to_string(Allocator const& a = {}) const
     {
         char buf[max_str_len];
         auto const n = print_impl(buf);
         char* dest;
-        string_value s(n, a, dest);
+        const_string s(n, a, dest);
         std::memcpy(dest, buf, n);
         return s;
     }
diff --git a/include/boost/url/params.hpp b/include/boost/url/params.hpp
index 4a94b3ed..85d0d16b 100644
--- a/include/boost/url/params.hpp
+++ b/include/boost/url/params.hpp
@@ -12,7 +12,7 @@
 
 #include <boost/url/detail/config.hpp>
 #include <boost/url/query_param.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <boost/url/detail/parts_base.hpp>
 #include <initializer_list>
 #include <iterator>
@@ -48,7 +48,7 @@ class params
         This is the allocator used to create read-only strings
         when iterators are dereferenced.
      */
-    string_value::allocator a_;
+    const_string::allocator a_;
 
     /** Construct query params from a url
 
@@ -110,7 +110,7 @@ public:
             char const* s,
             std::size_t nk,
             std::size_t nv,
-            string_value::allocator a);
+            const_string::allocator a);
 
     public:
         /** The query key.
@@ -119,7 +119,7 @@ public:
             holds the query key with percent-decoding
             applied.
         */
-        string_value key;
+        const_string key;
 
         /** The query value.
 
@@ -128,7 +128,7 @@ public:
             applied. The field @ref has_value indicates
             if the query value is defined.
         */
-        string_value value;
+        const_string value;
 
         /** True if the query parameter has a value.
 
@@ -270,7 +270,7 @@ public:
 
      */
     BOOST_URL_DECL
-    string_value
+    const_string
     at(string_view key) const;
 
     /** Access element at specified position without bounds checking
diff --git a/include/boost/url/params_encoded_view.hpp b/include/boost/url/params_encoded_view.hpp
index 8e99f6b6..3fc94021 100644
--- a/include/boost/url/params_encoded_view.hpp
+++ b/include/boost/url/params_encoded_view.hpp
@@ -119,7 +119,7 @@ public:
 
         This function returns a new view over the
         same underlying character buffer where each
-        segment is returned as a @ref string_value
+        segment is returned as a @ref const_string
         with percent-decoding applied using the
         optionally specified allocator.
 
diff --git a/include/boost/url/params_view.hpp b/include/boost/url/params_view.hpp
index 63e09f75..138a5156 100644
--- a/include/boost/url/params_view.hpp
+++ b/include/boost/url/params_view.hpp
@@ -11,7 +11,7 @@
 #define BOOST_URL_PARAMS_VIEW_HPP
 
 #include <boost/url/detail/config.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <boost/url/detail/parts_base.hpp>
 #include <iterator>
 #include <type_traits>
@@ -32,7 +32,7 @@ class params_view
 
     string_view s_;
     std::size_t n_;
-    string_value::allocator a_;
+    const_string::allocator a_;
 
     template<class Allocator>
     params_view(
@@ -58,8 +58,8 @@ public:
     class value_type
     {
     public:
-        string_value key;
-        string_value value;
+        const_string key;
+        const_string value;
         bool has_value;
 
         BOOST_URL_DECL
@@ -86,7 +86,7 @@ public:
             char const* s,
             std::size_t nk,
             std::size_t nv,
-            string_value::allocator a);
+            const_string::allocator a);
     };
 
     using reference = value_type;
@@ -101,7 +101,7 @@ public:
     //--------------------------------------------
 
     BOOST_URL_DECL
-    string_value
+    const_string
     at(string_view key) const;
 
     //--------------------------------------------
diff --git a/include/boost/url/pct_encoding.hpp b/include/boost/url/pct_encoding.hpp
index a7037b4c..6cf56cfb 100644
--- a/include/boost/url/pct_encoding.hpp
+++ b/include/boost/url/pct_encoding.hpp
@@ -12,7 +12,7 @@
 
 #include <boost/url/detail/config.hpp>
 #include <boost/url/error.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <boost/url/grammar/charset.hpp>
 #include <boost/url/rfc/charsets.hpp>
 #include <memory>
@@ -227,7 +227,7 @@ pct_decode(
     the given percent-encoded string, by
     converting escape sequences into their
     character equivalent.
-    The result is returned as a @ref string_value
+    The result is returned as a @ref const_string
     the optionally specified allocator.
 
     @par Exception Safety
@@ -270,7 +270,7 @@ pct_decode(
 template<
     class CharSet = reserved_chars_t,
     class Allocator = std::allocator<char> >
-string_value
+const_string
 pct_decode_to_value(
     string_view s,
     pct_decode_opts const& opt = {},
@@ -377,7 +377,7 @@ pct_decode_unchecked(
 */
 template<class Allocator =
     std::allocator<char> >
-string_value
+const_string
 pct_decode_unchecked(
     string_view s,
     pct_decode_opts const& opt = {},
@@ -580,7 +580,7 @@ pct_encode(
     the given plain string, by escaping all
     characters that are not in the specified
     <em>CharSet</em>.
-    The result is returned as a @ref string_value
+    The result is returned as a @ref const_string
     using the optionally specified allocator.
 
     @par Example
@@ -588,7 +588,7 @@ pct_encode(
     pct_encode_opts opt;
     opt.space_to_plus = true;
 
-    string_value s = pct_encode_to_value( "My Stuff", pchars, opt );
+    const_string s = pct_encode_to_value( "My Stuff", pchars, opt );
 
     assert( s == "My+Stuff" );
     @endcode
@@ -596,7 +596,7 @@ pct_encode(
     @par Exception Safety
     Calls to allocate may throw.
 
-    @return A @ref string_value holding the
+    @return A @ref const_string holding the
     encoded string.
 
     @param s The string to encode.
@@ -623,7 +623,7 @@ pct_encode(
 template<
     class CharSet = reserved_chars_t,
     class Allocator = std::allocator<char> >
-string_value
+const_string
 pct_encode_to_value(
     string_view s,
     pct_encode_opts const& opt = {},
diff --git a/include/boost/url/segments.hpp b/include/boost/url/segments.hpp
index 6cfe6905..bfa73832 100644
--- a/include/boost/url/segments.hpp
+++ b/include/boost/url/segments.hpp
@@ -11,7 +11,7 @@
 #define BOOST_URL_SEGMENTS_HPP
 
 #include <boost/url/detail/config.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <boost/url/detail/parts_base.hpp>
 #include <initializer_list>
 #include <iterator>
@@ -67,7 +67,7 @@ class segments
     : private detail::parts_base
 {
     url* u_ = nullptr;
-    string_value::allocator a_;
+    const_string::allocator a_;
 
     friend class url;
 
@@ -97,11 +97,11 @@ public:
         a segment where ownership is retained
         in the copy.
     */
-    using value_type = string_value;
+    using value_type = const_string;
 
-    using reference = string_value;
+    using reference = const_string;
 
-    using const_reference = string_value;
+    using const_reference = const_string;
 
     /** An unsigned integer type
     */
@@ -234,7 +234,7 @@ public:
         element.
     */
     inline
-    string_value
+    const_string
     at(std::size_t i) const;
 
     /** Return an element
@@ -256,20 +256,20 @@ public:
         element.
     */
     BOOST_URL_DECL
-    string_value
+    const_string
     operator[](
         std::size_t i) const;
 
     /** Return the first element
     */
     inline
-    string_value
+    const_string
     front() const;
 
     /** Return the last element
     */
     inline
-    string_value
+    const_string
     back() const;
 
     //--------------------------------------------
diff --git a/include/boost/url/segments_encoded_view.hpp b/include/boost/url/segments_encoded_view.hpp
index 1e2d4cf4..812df5f5 100644
--- a/include/boost/url/segments_encoded_view.hpp
+++ b/include/boost/url/segments_encoded_view.hpp
@@ -144,7 +144,7 @@ public:
 
         This function returns a new view over the
         same underlying character buffer where each
-        segment is returned as a @ref string_value
+        segment is returned as a @ref const_string
         with percent-decoding applied using the
         optionally specified allocator.
 
diff --git a/include/boost/url/segments_view.hpp b/include/boost/url/segments_view.hpp
index 7b27eeb6..6d833eb1 100644
--- a/include/boost/url/segments_view.hpp
+++ b/include/boost/url/segments_view.hpp
@@ -11,7 +11,7 @@
 #define BOOST_URL_SEGMENTS_VIEW_HPP
 
 #include <boost/url/detail/config.hpp>
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include <cstddef>
 #include <iosfwd>
 
@@ -32,7 +32,7 @@ class segments_view
 {
     string_view s_;
     std::size_t n_ = 0;
-    string_value::allocator a_;
+    const_string::allocator a_;
 
     friend class url_view;
     friend class segments_encoded_view;
@@ -54,15 +54,15 @@ public:
 
     /** The type of value returned when dereferencing an iterator.
     */
-    using value_type = string_value;
+    using value_type = const_string;
 
     /** The type of value returned when dereferencing an iterator.
     */
-    using reference = string_value;
+    using reference = const_string;
 
     /** The type of value returned when dereferencing an iterator.
     */
-    using const_reference = string_value;
+    using const_reference = const_string;
 
     /** The unsigned integer type used to represent size.
     */
@@ -104,13 +104,13 @@ public:
     /** Return the first element.
     */
     inline
-    string_value
+    const_string
     front() const noexcept;
 
     /** Return the last element.
     */
     inline
-    string_value
+    const_string
     back() const noexcept;
 
     //--------------------------------------------
diff --git a/include/boost/url/string.hpp b/include/boost/url/string.hpp
deleted file mode 100644
index ab6545a0..00000000
--- a/include/boost/url/string.hpp
+++ /dev/null
@@ -1,92 +0,0 @@
-//
-// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-// Official repository: https://github.com/CPPAlliance/url
-//
-
-#ifndef BOOST_URL_STRING_HPP
-#define BOOST_URL_STRING_HPP
-
-#include <boost/url/detail/config.hpp>
-#include <boost/url/string_view.hpp>
-#include <boost/type_traits/make_void.hpp>
-#include <memory>
-#include <string>
-#include <type_traits>
-
-namespace boost {
-namespace urls {
-
-/** A read-only, reference counted string
-
-    Objects of this type represent read-only
-    strings with ownership of the character
-    buffer. They are reference counted which
-    makes copies cheap. The type is derived
-    from @ref string_view which provides
-    compatibility with strings in terms of
-    comparisons and converisons. However,
-    care must be exercised; undefined
-    behavior results if the string_view
-    portion of the object is modified
-    directly, for example by calling
-    `remove_suffix` or `operator=`.
-
-    Slicing however, is supported, as
-    copies of the `string_view` portion
-    of the object are valid and remain
-    valid for the lifetime of the oriignal
-    object.
-*/
-class string_value : public string_view
-{
-    struct base;
-
-    base* p_ = nullptr;
-
-    template<class Allocator>
-    base*
-    construct(
-        std::size_t n,
-        Allocator const& a,
-        char*& dest);
-
-public:
-    class allocator;
-
-    inline
-    ~string_value();
-
-    string_value() = default;
-
-    template<class Allocator>
-    string_value(
-        std::size_t n,
-        Allocator const& a,
-        char*& dest);
-
-    template< class Allocator =
-        std::allocator<char> >
-    explicit
-    string_value(
-        string_view s,
-        Allocator const& a = {});
-
-    inline
-    string_value(
-        string_value const& other) noexcept;
-
-    inline
-    string_value&
-    operator=(string_value const& other) & noexcept;
-};
-
-} // urls
-} // boost
-
-#include <boost/url/impl/string.hpp>
-
-#endif
diff --git a/include/boost/url/url_view.hpp b/include/boost/url/url_view.hpp
index b9e94be8..ddeb5a61 100644
--- a/include/boost/url/url_view.hpp
+++ b/include/boost/url/url_view.hpp
@@ -719,7 +719,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -733,7 +733,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     userinfo(
         Allocator const& a = {}) const
     {
@@ -809,7 +809,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -825,7 +825,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     user(
         Allocator const& a = {}) const
     {
@@ -925,7 +925,7 @@ public:
         allocator is used, and the return type of
         the function becomes `std::string`.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -941,7 +941,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     password(
         Allocator const& a = {}) const
     {
@@ -1077,7 +1077,7 @@ public:
         the default allocator is used, and the return
         type of the function becomes `std::string`.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -1095,7 +1095,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     host(
         Allocator const& a = {}) const
     {
@@ -1105,7 +1105,7 @@ public:
             urls::host_type::name)
         {
             // no decoding
-            return string_value(s0, a);
+            return const_string(s0, a);
         }
         pct_decode_opts opt;
         opt.plus_to_space = false;
@@ -1527,7 +1527,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @par Specification
@@ -1541,7 +1541,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     query(
         Allocator const& a = {}) const
     {
@@ -1683,7 +1683,7 @@ public:
         string will use. If this parameter is omitted,
         the default allocator is used.
 
-        @return A @ref string_value using the
+        @return A @ref const_string using the
         specified allocator.
 
         @see
@@ -1693,7 +1693,7 @@ public:
     template<
         class Allocator =
             std::allocator<char>>
-    string_value
+    const_string
     fragment(
         Allocator const& a = {}) const
     {
diff --git a/test/unit/CMakeLists.txt b/test/unit/CMakeLists.txt
index 2f6ea382..5a7ce1ae 100644
--- a/test/unit/CMakeLists.txt
+++ b/test/unit/CMakeLists.txt
@@ -38,7 +38,7 @@ set(BOOST_URL_TESTS_FILES
     segments_view.cpp
     static_pool.cpp
     static_url.cpp
-    string.cpp
+    const_string.cpp
     string_view.cpp
     url.cpp
     url_view.cpp
diff --git a/test/unit/Jamfile b/test/unit/Jamfile
index d1c38392..9a973e43 100644
--- a/test/unit/Jamfile
+++ b/test/unit/Jamfile
@@ -42,7 +42,7 @@ local SOURCES =
     segments_view.cpp
     static_pool.cpp
     static_url.cpp
-    string.cpp
+    const_string.cpp
     string_view.cpp
     url.cpp
     url_view.cpp
diff --git a/test/unit/string.cpp b/test/unit/const_string.cpp
similarity index 91%
rename from test/unit/string.cpp
rename to test/unit/const_string.cpp
index c6793b48..47021d7b 100644
--- a/test/unit/string.cpp
+++ b/test/unit/const_string.cpp
@@ -8,7 +8,7 @@
 //
 
 // Test that header file is self-contained.
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 
 #include "test_suite.hpp"
 
@@ -26,7 +26,7 @@ public:
     void
     run()
     {
-        string_value sv("hello");
+        const_string sv("hello");
         auto sv2 = sv;
         BOOST_TEST(sv2 == sv);
         sv = {};
diff --git a/test/unit/pct_encoding.cpp b/test/unit/pct_encoding.cpp
index e8cd46ff..fe18faa4 100644
--- a/test/unit/pct_encoding.cpp
+++ b/test/unit/pct_encoding.cpp
@@ -118,7 +118,7 @@ public:
             }
             // pct_decode_to_value()
             {
-                string_value s =
+                const_string s =
                     pct_decode_to_value(
                         s0, opt, *pcs);
                 BOOST_TEST(s == s1);
@@ -126,7 +126,7 @@ public:
             // pct_decode_to_value(Allocator)
             {
                 static_pool<256> p;
-                string_value s =
+                const_string s =
                     pct_decode_to_value(
                         s0, opt, *pcs,
                             p.allocator());
diff --git a/test/unit/segments_view.cpp b/test/unit/segments_view.cpp
index dbb2ea9a..e6ec517f 100644
--- a/test/unit/segments_view.cpp
+++ b/test/unit/segments_view.cpp
@@ -88,7 +88,7 @@ public:
             sv = f(s).value().decoded(sp.allocator()));
         // forward
         {
-            std::vector<string_value> v1;
+            std::vector<const_string> v1;
             std::copy(
                 sv.begin(),
                 sv.end(),
@@ -97,7 +97,7 @@ public:
         }
         // reverse
         {
-            std::vector<string_value> v1;
+            std::vector<const_string> v1;
             std::copy(
                 reverse(sv.end()),
                 reverse(sv.begin()),
diff --git a/test/unit/static_pool.cpp b/test/unit/static_pool.cpp
index 79d79c3a..7580de6e 100644
--- a/test/unit/static_pool.cpp
+++ b/test/unit/static_pool.cpp
@@ -10,7 +10,7 @@
 // Test that header file is self-contained.
 #include <boost/url/static_pool.hpp>
 
-#include <boost/url/string.hpp>
+#include <boost/url/const_string.hpp>
 #include "test_suite.hpp"
 
 #include <iostream>
@@ -24,13 +24,13 @@ public:
     template<class Allocator =
         std::allocator<char>>
     static
-    string_value
+    const_string
     make_string(
         string_view s,
         Allocator const& a = {})
     {
         char* dest;
-        string_value sv(
+        const_string sv(
             s.size(), a, dest);
         std::memcpy(dest,
             s.data(), s.size());