Is typename / class needed when declaring template

Question

When declaring template params is typename / class necessary (as in language could not work with diff syntax I suggest below) . I know template params can be integers so you would have to pick to default to int or to typename / class but still.

i.e. why not

template <T>
T max(T a, T b) {
    return a > b ? a : b;
}

instead of

template <typename T>
T max(T a, T b) {
    return a > b ? a : b;
}

and

template<T, size_t n>
size_t array_size(const T (&)[n]) {
    return n;
}

instead of

template<typename T, size_t n>
size_t array_size(const T (&)[n]) {
    return n;
}

Answer 1

The language could certainly still work if template parameters defaulted to being types; just as C used to work when variable types defaulted to int in the absence of a type specifier. There would be some ambiguities to overcome, for example:

typedef int T;
template <T> class C;  // type, or non-type value of type `T`?

However, forcing you to be explicit allows much better diagnostics. If I forget to specify the type of a non-type parameter, then the compiler can immediately spot the mistake and tell me about it. In your world, it would assume I intended a type parameter, and carry on trying to interpret the template accordingly; probably producing confusing errors, or perhaps even successfully compiling something that does completely the wrong thing.

I can't comment on whether that's the reason for not allowing a default here (or for removing default variable types from C, or for never allowing them in C++), but it's certainly a good enough reason for me.