Question

I was interested to note that C++ (VSVC++ 2008 specifically) lets me declare a struct inline in a method.
e.g:

MyClass::method()
{
 struct test{ int x;};
 test t = {99};
}

My question is, how does this declaration work internally, and specifically does it have any negative performance implications?

Answer 1

how does this declaration work internally?

Exactly like a declaration at namespace scope, except that the name is only visible within the scope of the block it’s declared in (in this case, the function body). UPDATE: as @Nawaz points out, there are one or two extra restrictions that apply to local classes: they cannot have static data members, and (in C++03, but not C++11) they can’t be used as template type arguments.

does it have any negative performance implications?

No, apart from its scope (which only affects whether or not the code compiles), it is identical to any other class definition.