documentation and examples

example/make_function.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)
+->*/
+
+//[ make_function
+#include <functional>
+#include <callable_traits/callable_traits.hpp>
+
+namespace example_library {
+
+    namespace ct = callable_traits;
+
+    //make_function turns a non-overloaded callable into a type-erased std::function object
+    template<typename T>
+    inline decltype(auto) make_function(T&& t) {
+
+        // callable_traits::function_type decays any non-overloaded callable type to
+        // a plain function type, which is structured in terms of INVOKE.
+
+        using signature = ct::function_type<T&&>;
+        using result_type = std::function<signature>;
+        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) {
+
+        // callable_traits::bind is essentially a compile-time parser of placeholders
+        // expressions, for the purpose of retaining more type information than
+        // std::bind normally allows - specifically, callable_traits::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, callable_traits::bind
+        // is also a thin forwarding wrapper around std::bind (which is the only true
+        // runtime element in CallableTraits).
+
+        using bind_expr = decltype(ct::bind(
+                std::forward<T>(t),
+                std::forward<First>(first),
+                std::forward<Others>(others)...
+        ));
+
+        using signature = ct::function_type<bind_expr>;
+        using result_type = std::function<signature>;
+
+        return result_type{ std::bind(
+                std::forward<T>(t),
+                std::forward<First>(first),
+                std::forward<Others>(others)...
+        )};
+    }
+}
+
+//client code starts here
+#include <cassert>
+
+using namespace example_library;
+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);
+}
+//]