Why can a pointer to a function be called without dereferencing?

I have a weird typedef statement in a C++ program, generated by Py++.

double radius(int);  // function to be wrapped
typedef double (*radius_function_type)(int);

// bp::def is a function for wrapping    
bp::def("radius", radius_function_type(&radius));

I have figured out that the typedef statement above is not of the familiar form:

typedef complex_type simple_alias;

Rather it is a way to declare pointer to a function which takes int as argument and returns double (same as the prototype).

So how can this pointer to a function (without dereferencing) be called with the address of a function as an argument? This also doesn't match with the prototype. Somebody please explain!

Your question is confusing. Are you asking what this does:

radius_function_type(&radius)"

This is just a C++ typecast, a bit like:

radius (int (42));

but since radius is already of type radius_function_type then you can just as easily do:

bp::def("radius", radius);

but as this is code generated by Py++, it's probably being extra careful with the output.