C++’s most vexing parse again [duplicate]

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In a function declaration, arguments of type array decay into pointers to the first element, arguments of type function decay into a function pointer, so the signature would be:

widget w( gadget(*)(), doodad(*)() );

That is, a function that takes as the first argument a pointer to a function taking no arguments and returning gadget, that takes as second argument a pointer to a function taking no arguments and returning a doodad and that the function itself returns a widget

There are even more interesting or confusing cases, like:

// assume 'x' is a variable defined somewhere:
widget w(gadget(x));

How could that be interpreted as a function declaration? I mean, x is a variable, right? Well, when declaring a variable you can add extra parenthesis, so gadget x; and gadget (x); both declare the same variable x. The same applies to function arguments so the code above looks like a declaration of a function that takes a first argument named x of type gadget and returns a widget…

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