std::tr1::function and the template value it accepts

Question

I was reviewing some code and came upon a line similar to:

std::tr1::function<bool (int, int)>(//etc...

The syntax for the template type, bool (int, int) was unfamiliar to me. Based on Googling, in the case of std::tr1::function it seems this syntax is used to define a function's return type and parameters. That makes sense, but why does that syntax work? As far as I know, C++ templates can only specify types?

I tried to instantiate an instance of the type in code as:

bool (int, int) test;

As I expected, the statement failed to compile. At the very least, the syntax would need to be something like: bool (test)(int, int);

Is bool (int, int) treated as a C++ type? Any tips on reconciling this in my mind?

Thanks, Adam

Answer 1

It is called a function type.

You can't create instances of it, but you can create pointers to them and typedefs.

This question has some insight: What is a function type used for?