An implementation of function_ref.
A lightweight non-owning reference to a callable.
Example:
void foo (function_ref<int(int)> func) {
std::cout << "Result is " << func(21); //42
}
foo([](int i) { return i*2; });
Specialization for function types.
Special Members
.. function:: constexpr function_ref() noexcept = delete
.. function:: constexpr function_ref(function_ref const &rhs) noexcept
Creates a `tl::function_ref` which refers to the same callable as `rhs`.
.. function:: template <typename F> constexpr function_ref(F &&f) noexcept
Creates a `tl::function_ref` which refers to `f`.
`f` must be invocable with `Args...`, returning a type convertible to `R`.
.. function:: function_ref & operator=(function_ref const &rhs) noexcept
Makes `*this` refer to the same callable as `rhs`.
.. function:: template <typename F> constexpr function_ref &operator=(F &&f) noexcept
Makes `*this` refer to `f`.
`f` must be invocable with `Args...`, returning a type convertible to `R`.
.. function:: constexpr void swap(function_ref &rhs) noexcept
Swaps the callables referred to by `*this` and `rhs`.
.. function:: R operator()(Args... args) const
Invoke the stored callable with the given arguments.
.. function:: template <typename R, typename... Args>\
constexpr void swap(function_ref<R(Args...)> &lhs,\
function_ref<R(Args...)> &rhs) noexcept
Swaps the callables referred to by `*this` and `rhs`.