Replace std::function with hyper_function for a 37% speedup in compile time.

Before:

    time c++ -O2 -DMAC -I/usr/local/include -std=c++11 -march=native
             -W -Wall -Wextra -Werror -pedantic -Wno-format-pedantic
             -Wno-missing-field-initializers -Wno-unused-parameter
             -DCAP_GLEW=0 -DCAP_PNG=0    -c hyper.cpp -o hyper.o

    real 2m22.508s
    user 2m20.625s
    sys  0m1.648s

After:

    time c++ -O2 -DMAC -I/usr/local/include -std=c++11 -march=native
             -W -Wall -Wextra -Werror -pedantic -Wno-format-pedantic
             -Wno-missing-field-initializers -Wno-unused-parameter
             -DCAP_GLEW=0 -DCAP_PNG=0    -c hyper.cpp -o hyper.o

    real 1m30.515s
    user 1m29.793s
    sys  0m0.689s

Comparing object file size:

    -rw-r--r--  1 ajo  staff  8215036 Jan  5 20:46 old-hyper.o
    -rw-r--r--  1 ajo  staff  7538072 Jan  5 20:47 new-hyper.o

Comparing number of symbols:

    nm old-hyper.o | wc -l  => 12590
    nm new-hyper.o | wc -l  =>  9742

No appreciable difference in link time; the linker takes less than
half a second in either case.

hyper.h

@@ -7,6 +7,7 @@
 #define VERNUM_HEX 0xA505
 
 #include <stdarg.h>
+#include "hyper_function.h"
 
 namespace hr {
 
@@ -15,6 +16,8 @@ void ignore(T&&) {
   // placate GCC's overzealous -Wunused-result
   }
 
+template<class Sig> using function = hyper_function<Sig>;
+
 // functions and types used from the standard library
 using std::vector;
 using std::map;
@@ -24,7 +27,6 @@ using std::sort;
 using std::multimap;
 using std::set;
 using std::string;
-using std::function;
 using std::pair;
 using std::tuple;
 using std::shared_ptr;

hyper_function.h

@@ -0,0 +1,61 @@
+#pragma once
+
+#include <type_traits>
+#include <utility>
+
+template<class Sig>
+class hyper_function;
+
+template<class R, class... Args>
+struct hyper_function_state_base {
+    virtual R call(Args...) const = 0;
+    virtual hyper_function_state_base *clone() const = 0;
+    virtual ~hyper_function_state_base() = default;
+};
+
+template<class T, class R, class... Args>
+struct hyper_function_state : hyper_function_state_base<R, Args...> {
+    using Self = hyper_function_state<T, R, Args...>;
+    T t_;
+    explicit hyper_function_state(T t) : t_(std::move(t)) {}
+    R call(Args... args) const override {
+        return const_cast<T&>(t_)(static_cast<Args&&>(args)...);
+    }
+    hyper_function_state_base<R, Args...> *clone() const override {
+        return new Self(*this);
+    }
+};
+
+template<class R, class... Args>
+class hyper_function<R(Args...)>
+{
+    hyper_function_state_base<R, Args...> *ptr_ = nullptr;
+public:
+    hyper_function() = default;
+
+    template<class Callable, class = decltype(R(std::declval<typename std::decay<Callable>::type>()(std::declval<Args>()...)))>
+    hyper_function(Callable&& t) :
+        ptr_(new hyper_function_state<typename std::decay<Callable>::type, R, Args...>(static_cast<Callable&&>(t)))
+    {}
+
+    ~hyper_function() {
+        delete ptr_;
+    }
+
+    hyper_function(hyper_function& rhs) : ptr_(rhs.ptr_ ? rhs.ptr_->clone() : nullptr) {}
+    hyper_function(const hyper_function& rhs) : ptr_(rhs.ptr_ ? rhs.ptr_->clone() : nullptr) {}
+    hyper_function(hyper_function&& rhs) noexcept : ptr_(rhs.ptr_) { rhs.ptr_ = nullptr; }
+    hyper_function(const hyper_function&& rhs) = delete;
+
+    void operator=(hyper_function rhs) noexcept {
+        std::swap(ptr_, rhs.ptr_);
+    }
+
+    R operator()(Args... args) const {
+        return ptr_->call(static_cast<Args&&>(args)...);
+    }
+
+    explicit operator bool() const noexcept {
+        return ptr_ != nullptr;
+    }
+};