adding license, make_function example

LICENSE.md

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+Copyright 2015-2016 Barrett Adair
+
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.

test/make_function.hpp

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+/*<-
+Copyright Barrett Adair 2016
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http ://boost.org/LICENSE_1_0.txt)
+->*/
+
+#ifndef EXAMPLE_MAKE_FUNCTION_HPP
+#define EXAMPLE_MAKE_FUNCTION_HPP
+
+#include <functional>
+#include <type_traits>
+#include <utility>
+
+#include "bind_parser.hpp"
+
+namespace example {
+
+    // make_function turns a non-overloaded callable into a type-erased std::function object
+    template<typename T>
+    inline decltype(auto) make_function(T&& t) {
+
+        using no_ref = typename std::remove_reference<T>::type;
+        using f = bind_parser::function_type<no_ref>;
+        using result_type = std::function<f>;
+        return result_type{ std::forward<T>(t) };
+    }
+
+    // this make_function overload turns a bind expression into a type-erased std::function object
+    template<typename T, typename First, typename... Others>
+    inline decltype(auto) make_function(T&& t, First&& first, Others&&... others) {
+
+        // bind_parser::bind is a compile-time parser of placeholder expressions,
+        // for the purpose of retaining more type information than std::bind normally
+        // allows - specifically,  bind_parser::bind is used to determine the de-facto
+        // signature of the std::bind return type, with special considerations for
+        // conversions between reused placeholders and nested placeholder expressions.
+        //  For the sake of convenience, bind_parser::bind is also a thin forwarding
+        // wrapper around std::bind.
+
+        using bind_expr = decltype(bind_parser::bind(
+                std::forward<T>(t),
+                std::forward<First>(first),
+                std::forward<Others>(others)...
+        ));
+
+        using f = bind_parser::function_type<bind_expr>;
+        using result_type = std::function<f>;
+
+        return result_type{ std::bind(
+                std::forward<T>(t),
+                std::forward<First>(first),
+                std::forward<Others>(others)...
+        )};
+    }
+}

test/make_function_example.cpp

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+/*<-
+Copyright Barrett Adair 2016
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http ://boost.org/LICENSE_1_0.txt)
+->*/
+
+#undef NDEBUG
+
+#include <cassert>
+#include <functional>
+
+#include "make_function.hpp"
+
+using namespace example;
+using namespace std::placeholders;
+
+int add(int i, int j) {
+    return i + j;
+}
+
+struct adder {
+
+    int eval(int i, int j) const { return i + j; }
+};
+
+int main() {
+
+    // function pointer
+    auto f = make_function(&add);
+    assert(f(99, 1) == 100);
+
+    // function reference
+    f = make_function(add);
+    assert(f(99, 1) == 100);
+
+    // member function pointer (bound to object)
+    f = make_function(&adder::eval, adder{}, _1, _2);
+    assert(f(99, 1) == 100);
+
+    // lambda
+    f = make_function([](int i, int j) {
+        return i + j;
+    });
+
+    assert(f(99, 1) == 100);
+}