defer - A Go-like deferred lambda invocation for c++

Golang has a very convenient defer operator allowing us to, obviously, defer execution of a lambda until the scope termination.

This header-only library lets us use it in c++ programs. Just include it and start deferring.

Why do we need it at all? Are destructors insufficient?

For example, when we interoperate with older libraries or OS features and obtain resource handles that must be cleaned up manually and in unpredictable ways. Setting up a specific wrapper object to utilize RAII looks like unnecessary complication.

Consider Win32 call CreateSolidBrush. The HBRUSH handle it returns must be deleted with DeleteObject.

	// Initialize the deferrer
	maxy::control::Defer defer {};

	// Obtain the handle in question
	HBRUSH brush = CreateSolidBrush (RGB (255,128,0));

	// Schedule handle release to be performed at the return.
	defer ([=] () { DeleteObject (brush); });

	// A long chunk of code with multiple returns follows.
	// We don't bother deleting our handle explicitly at each return.

See main.cpp for more examples.