Understanding complex typedef expressions [duplicate]

Question

I'd like to know what this expression means??

typedef bool (*compareShapes)(const Shape* s1, const Shape* s2);

The Shape is a class.

Answer 1

You should be using using-statements. It make the very same declaration easier to read:

using compareShapes = bool(*)(const Shape*, const Shape*);

See it now? the type is after the equal sign. It's a pointer to function type.

One could declare it like this too:

// function pointer type --v----------------------------------------------------v
using compareShapes =      std::add_pointer_t< bool(const Shape*, const Shape*) >;
//                    function signature  -----^------------------------------^

The function signature is composed like this:

<return-type>( <arguments...> )

When you add the pointer in it, it looks like this:

<return-type>(*)( <arguments...> )

And if you add the pointer name or type name here, add it after the star:

<return-type>(*typeOrPointerName)( <arguments...> )