Provide a way to specify radix, and min/max digits for {u,}int_parser, without

using the template parameters directly, since this also requires the user to
type parser_interface.

Fixes #220.

doc/tables.qbk

@@ -230,7 +230,7 @@ the input they match unless otherwise stated in the table below.]
     [[ _ui_ ]
      [ Matches an unsigned integral value. ]
      [ `unsigned int` ]
-     []]
+     [ To specify a base/radix of `N`, use _ui_`.base<N>()`.  To specify exactly `D` digits, use _ui_`.digits<D>()`.  To specify a minimum of `LO` digits and a maximum of `HI` digits, use _ui_`.digits<LO, HI>()`.  These calls can be chained, as in _ui_`.base<2>().digits<8>()`. ]]
 
     [[ `_ui_(arg0)` ]
      [ Matches exactly the unsigned integral value `_RES_np_(arg0)`. ]
@@ -270,7 +270,7 @@ the input they match unless otherwise stated in the table below.]
     [[ _i_ ]
      [ Matches a signed integral value. ]
      [ `int` ]
-     []]
+     [ To specify a base/radix of `N`, use _i_`.base<N>()`.  To specify exactly `D` digits, use _i_`.digits<D>()`.  To specify a minimum of `LO` digits and a maximum of `HI` digits, use _i_`.digits<LO, HI>()`.  These calls can be chained, as in _i_`.base<2>().digits<8>()`. ]]
 
     [[ `_i_(arg0)` ]
      [ Matches exactly the signed integral value `_RES_np_(arg0)`. ]

doc/tutorial.qbk

@@ -1248,22 +1248,25 @@ these parsers is in a subsequent section.  The attributes are repeated here so
 you can use see all the properties of the parsers in one place.]
 
 If you have an integral type `IntType` that is not covered by any of the
-_Parser_ parsers, you can use a more verbose declaration to declare a parser
-for `IntType`.  If `IntType` were unsigned, you would use `uint_parser`.  If
-it were signed, you would use `int_parser`.  For example:
+_Parser_ parsers, you can explicitly specify a base/radix or bounds on the
+number of digits.  You do this by calling the `base()` and `digits()` member
+functions on an existing parser of the right intgral type.  So if `IntType`
+were unsigned, you would use `uint_`.  If it were signed, you would use
+`int_`.  For example:
 
-    constexpr parser_interface<int_parser<IntType>> hex_int;
+    constexpr auto hex_int = bp::uint_.base<16>();
 
-`uint_parser` and `int_parser` accept three more non-type template parameters
-after the type parameter.  They are `Radix`, `MinDigits`, and `MaxDigits`.
-`Radix` defaults to `10`, `MinDigits` to `1`, and `MaxDigits` to `-1`, which
-is a sentinel value meaning that there is no max number of digits.
+You simply chain together the contraints you want to use, like
+`.base<16>().digits<2>()` or .digits<4>().base<8>()`.
 
 So, if you wanted to parse exactly eight hexadecimal digits in a row in order
 to recognize Unicode character literals like C++ has (e.g. `\Udeadbeef`), you
 could use this parser for the digits at the end:
 
-    constexpr parser_interface<uint_parser<unsigned int, 16, 8, 8>> hex_int;
+    constexpr auto hex_4_def = bp::uint_.base<16>().digits<8>();
+
+If you want to specify an acceptable range of digits, use `.digits<LO, HI>()`.
+Both `HI` and `LO` are inclusive bounds.
 
 [endsect]
 

example/callback_json.cpp

@@ -126,7 +126,7 @@ namespace json {
         }
     };
 
-    bp::parser_interface<bp::uint_parser<uint32_t, 16, 4, 4>> const hex_4_def;
+    auto const hex_4_def = boost::parser::uint_.base<16>().digits<4>();
 
     auto const escape_seq_def = "\\u" > hex_4;
 

example/json.cpp

@@ -151,12 +151,10 @@ namespace json {
         }
     };
 
-    // This is the verbose form of declaration for the integer and unsigned
-    // integer parsers int_parser and uint_parser.  In this case, we don't
-    // want to use boost::parser::hex directly, since it has a variable number
-    // of digits.  We want to match exactly 4 digits, and this is how we
-    // declare a hexadecimal parser that matches exactly 4.
-    bp::parser_interface<bp::uint_parser<uint32_t, 16, 4, 4>> const hex_4_def;
+    // We don't want to use boost::parser::hex directly, since it has a
+    // variable number of digits.  We want to match exactly 4 digits, and this
+    // is how we declare a hexadecimal parser that matches exactly 4.
+    auto const hex_4_def = boost::parser::uint_.base<16>().digits<4>();
 
     // We use > here instead of >>, because once we see \u, we know that
     // exactly four hex digits must follow -- no other production rule starts

include/boost/parser/parser.hpp

@@ -5421,6 +5421,29 @@ namespace boost { namespace parser {
 
 #endif
 
+    namespace detail {
+        template<typename T>
+        using base_member_function_template_expr =
+            decltype(std::declval<T>().template base<2>());
+        template<typename T>
+        constexpr bool has_base_member_function_template_v =
+            is_detected_v<base_member_function_template_expr, T>;
+
+        template<typename T>
+        using has_digits1_member_function_template_expr =
+            decltype(std::declval<T>().template digits<1>());
+        template<typename T>
+        constexpr bool has_digits1_member_function_template_v =
+            is_detected_v<has_digits1_member_function_template_expr, T>;
+
+        template<typename T>
+        using has_digits2_member_function_template_expr =
+            decltype(std::declval<T>().template digits<1, 2>());
+        template<typename T>
+        constexpr bool has_digits2_member_function_template_v =
+            is_detected_v<has_digits2_member_function_template_expr, T>;
+    }
+
     // Parser interface.
 
     template<typename Parser, typename GlobalState, typename ErrorHandler>
@@ -5760,7 +5783,7 @@ namespace boost { namespace parser {
             return parser_.call(first, last, context, skip, flags, success);
         }
 
-        /** Applies `parser_`, assiging the parsed attribute, if any, to
+        /** Applies `parser_`, assinging the parsed attribute, if any, to
             `attr`, unless the attribute is reported via callback. */
         template<
             typename Iter,
@@ -5780,6 +5803,60 @@ namespace boost { namespace parser {
             parser_.call(first, last, context, skip, flags, success, attr);
         }
 
+        /** Returns a new `parser_interface` constructed from
+            `parser_.base<Radix2>()`.  Note that this only works for integral
+            numeric parsers like `int_` and `uint_`. */
+        template<int Radix2>
+        constexpr auto base() const noexcept
+        {
+            if constexpr (detail::has_base_member_function_template_v<
+                              parser_type>) {
+                return parser::parser_interface{
+                    parser_.template base<Radix2>()};
+            } else {
+                static_assert(
+                    detail::has_base_member_function_template_v<parser_type>,
+                    "Only certain parsers have a .base<>() member function. "
+                    "This is not one of them.");
+            }
+        }
+
+        /** Returns a new `parser_interface` constructed from
+            `parser_.digits<Digits>()`.  Note that this only works for
+            integral numeric parsers like `int_` and `uint_`. */
+        template<int Digits>
+        constexpr auto digits() const noexcept
+        {
+            if constexpr (detail::has_digits1_member_function_template_v<
+                              parser_type>) {
+                return parser::parser_interface{
+                    parser_.template digits<Digits>()};
+            } else {
+                static_assert(
+                    detail::has_digits1_member_function_template_v<parser_type>,
+                    "Only certain parsers have a .base<>() member function. "
+                    "This is not one of them.");
+            }
+        }
+
+        /** Returns a new `parser_interface` constructed from
+            `parser_.digits<MinDigits2, MaxDigits2>()`.  Note that this only
+            works for integral numeric parsers like `int_` and `uint_`. */
+        template<int MinDigits2, int MaxDigits2>
+        constexpr auto digits() const noexcept
+        {
+            if constexpr (detail::has_digits2_member_function_template_v<
+                              parser_type>) {
+                return parser::parser_interface{
+                    parser_.template digits<MinDigits2, MaxDigits2>()};
+            } else {
+                static_assert(
+                    detail::has_digits2_member_function_template_v<parser_type>,
+                    "Only certain parsers have a .base<>() member function. "
+                    "This is not one of them.");
+            }
+        }
+
         parser_type parser_;
         global_state_type globals_;
         error_handler_type error_handler_;
@@ -7926,7 +8003,11 @@ namespace boost { namespace parser {
         typename Expected>
     struct uint_parser
     {
-        static_assert(2 <= Radix && Radix <= 36, "Unsupported radix.");
+        static_assert(
+            Radix == 2 || Radix == 8 || Radix == 10 || Radix == 16,
+            "Unsupported radix.");
+        static_assert(1 <= MinDigits);
+        static_assert(MaxDigits == -1 || MinDigits <= MaxDigits);
 
         constexpr uint_parser() {}
         explicit constexpr uint_parser(Expected expected) : expected_(expected)
@@ -7992,6 +8073,33 @@ namespace boost { namespace parser {
             return parser_interface{parser_t{expected}};
         }
 
+        /** Returns a `uint_parser` identical to `*this`, except that it
+            parses digits as base-`Radix2` instead of base-`Radix`. */
+        template<int Radix2>
+        constexpr auto base() const noexcept
+        {
+            return uint_parser<T, Radix2, MinDigits, MaxDigits, Expected>{
+                expected_};
+        }
+
+        /** Returns a `uint_parser` identical to `*this`, except that it only
+            accepts numbers exactly `Digits` digits. */
+        template<int Digits>
+        constexpr auto digits() const noexcept
+        {
+            return uint_parser<T, Radix, Digits, Digits, Expected>{expected_};
+        }
+
+        /** Returns a `uint_parser` identical to `*this`, except that it
+            only accepts numbers `D` digits long, where `D` is in
+            [`MinDigits2`, MaxDigits2`]. */
+        template<int MinDigits2, int MaxDigits2>
+        constexpr auto digits() const noexcept
+        {
+            return uint_parser<T, Radix, MinDigits2, MaxDigits2, Expected>{
+                expected_};
+        }
+
         Expected expected_;
     };
 
@@ -8039,6 +8147,8 @@ namespace boost { namespace parser {
         static_assert(
             Radix == 2 || Radix == 8 || Radix == 10 || Radix == 16,
             "Unsupported radix.");
+        static_assert(1 <= MinDigits);
+        static_assert(MaxDigits == -1 || MinDigits <= MaxDigits);
 
         constexpr int_parser() {}
         explicit constexpr int_parser(Expected expected) : expected_(expected)
@@ -8104,6 +8214,33 @@ namespace boost { namespace parser {
             return parser_interface{parser_t{expected}};
         }
 
+        /** Returns an `int_parser` identical to `*this`, except that it
+            parses digits as base-`Radix2` instead of base-`Radix`. */
+        template<int Radix2>
+        constexpr auto base() const noexcept
+        {
+            return int_parser<T, Radix2, MinDigits, MaxDigits, Expected>{
+                expected_};
+        }
+
+        /** Returns an `int_parser` identical to `*this`, except that it only
+            accepts numbers exactly `Digits` digits. */
+        template<int Digits>
+        constexpr auto digits() const noexcept
+        {
+            return int_parser<T, Radix, Digits, Digits, Expected>{expected_};
+        }
+
+        /** Returns an `int_parser` identical to `*this`, except that it
+            only accepts numbers `D` digits long, where `D` is in
+            [`MinDigits2`, MaxDigits2`]. */
+        template<int MinDigits2, int MaxDigits2>
+        constexpr auto digits() const noexcept
+        {
+            return int_parser<T, Radix, MinDigits2, MaxDigits2, Expected>{
+                expected_};
+        }
+
         Expected expected_;
     };
 

include/boost/parser/parser_fwd.hpp

@@ -404,8 +404,8 @@ namespace boost { namespace parser {
         and at most `MaxDigits`, producing an attribute of type `T`.  Fails on
         any other input.  The parse will also fail if `Expected` is anything
         but `detail::nope` (which it is by default), and the produced
-        attribute is not equal to `expected_`.  `Radix` must be in `[2,
-        36]`. */
+        attribute is not equal to `expected_`.  `Radix` must be one of `2`,
+        `8`, `10`, or `16`. */
     template<
         typename T,
         int Radix = 10,