Destructors of builtin types (int, char etc..)

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It’s the reason that makes your code work for generic parameters. Consider a container C:

template<typename T>
struct C {
    // ...
    ~C() {
        for(size_t i = 0; i<elements; i++)
            buffer[i].~T();
    }
};

It would be annoying to introduce special cases for built-in types. So C++ allows you to do the above, even if T happens to equal to int. The holy Standard says in 12.4 p15:

The notation for explicit call of a destructor can be used for any scalar type name. Allowing this makes it possible to write code without having to know if a destructor exists for a given type.

The difference between using a plain int and a typedef’ed int is that they are syntactically different things. The rule is, that in a destructor call, the thing after the ~ is a type-name. int is not such a thing, but a typedef-name is. Look it up in 7.1.5.2.

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