Merge pull request #14 from pfultz2/if

If

CMakeLists.txt

@@ -74,6 +74,7 @@ add_test_executable(flip)
 add_test_executable(flow)
 add_test_executable(function)
 add_test_executable(identity)
+add_test_executable(if)
 add_test_executable(implicit)
 add_test_executable(indirect)
 add_test_executable(infix)

fit/if.h

@@ -0,0 +1,109 @@
+/*=============================================================================
+    Copyright (c) 2015 Paul Fultz II
+    if_.h
+    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)
+==============================================================================*/
+
+#ifndef FIT_GUARD_IF_H
+#define FIT_GUARD_IF_H
+
+/// if
+/// ==
+/// 
+/// Description
+/// -----------
+/// 
+/// The `if_` function applies a boolen condition to the function.
+/// 
+/// Synopsis
+/// --------
+/// 
+///     template<class IntegralConstant>
+///     constexpr auto if_(IntegralConstant);
+/// 
+/// Requirements
+/// ------------
+/// 
+/// IntegralConstant must be:
+/// 
+///     IntegralConstant
+/// 
+/// Example
+/// -------
+/// 
+///     struct sum_f
+///     {
+///         template<class T>
+///         int operator()(T x, T y) const
+///         {
+///             return fit::conditional(
+///                 fit::if_(std::is_integral<T>())(fit::_ + fit::_),
+///                 fit::always(0)
+///             )(x, y);
+///         }
+///     };
+///     assert(sum_f()(1, 2) == 3);
+///     assert(sum_f()("", "") == 0);
+/// 
+
+#include <fit/always.h>
+#include <fit/detail/result_of.h>
+#include <fit/detail/forward.h>
+#include <fit/detail/delegate.h>
+#include <fit/detail/move.h>
+#include <fit/detail/static_const_var.h>
+
+namespace fit {
+
+namespace detail {
+
+template<class C, class...>
+struct if_depend
+: C
+{};
+
+template<bool Cond, class F>
+struct if_adaptor : F
+{
+    FIT_INHERIT_CONSTRUCTOR(if_adaptor, F)
+};
+
+template<class F>
+struct if_adaptor<false, F>
+{
+    template<class... Ts>
+    constexpr if_adaptor(Ts&&...)
+    {}
+};
+
+template<bool Cond>
+struct make_if_f
+{
+    constexpr make_if_f()
+    {}
+    template<class F>
+    constexpr if_adaptor<Cond, F> operator()(F f) const
+    {
+        return if_adaptor<Cond, F>(fit::move(f));
+    }
+};
+
+struct if_f
+{
+    constexpr if_f()
+    {}
+    template<class Cond, bool B=Cond::type::value>
+    constexpr make_if_f<B> operator()(Cond) const
+    {
+        return {};
+    }
+};
+
+}
+
+FIT_DECLARE_STATIC_VAR(if_, detail::if_f);
+
+}
+
+#endif

mkdocs.yml

@@ -49,6 +49,7 @@ pages:
     - 'eval': 'eval.md'
     - 'FIT_STATIC_FUNCTION': 'function.md'
     - 'FIT_STATIC_LAMBDA': 'lambda.md'
+    - 'if': 'if.md'
     - 'lift': 'lift.md'
     - 'is_callable': 'is_callable.md'
     - 'pack': 'pack.md'

test/if.cpp

@@ -0,0 +1,84 @@
+#include <fit/if.h>
+#include "test.h"
+
+#include <fit/conditional.h>
+#include <fit/placeholders.h>
+
+
+struct is_5
+{
+    template<class T>
+    constexpr bool operator()(T i) const
+    {
+        return i == 5;
+    }
+};
+
+struct is_not_5
+{
+    template<class T>
+    constexpr bool operator()(T i) const
+    {
+        return i != 5;
+    }
+};
+
+template<class F>
+struct test_int
+{
+    template<class T>
+    constexpr bool operator()(T x) const
+    {
+        return fit::conditional(
+            fit::if_(std::is_integral<T>())(F()),
+            fit::always(true)
+        )(x);
+    }
+};
+
+FIT_TEST_CASE()
+{
+    FIT_TEST_CHECK(test_int<is_5>()(5));
+    FIT_TEST_CHECK(test_int<is_5>()(5L));
+    FIT_TEST_CHECK(test_int<is_5>()(5.0));
+    FIT_TEST_CHECK(test_int<is_5>()(6.0));
+
+    FIT_TEST_CHECK(test_int<is_not_5>()(6));
+    FIT_TEST_CHECK(test_int<is_not_5>()(6L));
+    FIT_TEST_CHECK(test_int<is_not_5>()(5.0));
+    FIT_TEST_CHECK(test_int<is_not_5>()(6.0));
+
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(5));
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(5L));
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(5.0));
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(6.0));
+
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6));
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6L));
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(5.0));
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6.0));
+}
+
+struct sum_f
+{
+    template<class T>
+    constexpr int operator()(T x, T y) const
+    {
+        return fit::conditional(
+            fit::if_(std::is_integral<T>())(fit::_ + fit::_),
+            fit::always(0)
+        )(x, y);
+    }
+};
+
+FIT_TEST_CASE()
+{
+    FIT_TEST_CHECK(sum_f()(1, 2) == 3);
+    FIT_TEST_CHECK(sum_f()(1.0, 2.0) == 0);
+    FIT_TEST_CHECK(sum_f()("", "") == 0);
+
+    FIT_STATIC_TEST_CHECK(sum_f()(1, 2) == 3);
+    FIT_STATIC_TEST_CHECK(sum_f()("", "") == 0);
+}
+
+