[tialaramex]

> //v[3] == 4 is true here

Note that C++ std::vector has an operator overload so this is actually just calling the method named operator[] on the object v and that method returns you a reference to the object in the backing array if in fact it is a suitable size (no checks are made). In particular if foo doesn't for any reason extend the vector then our program now has Undefined Behaviour.

This is not merely the C syntactic sugar array subscript operation v[3] == *(v+3) as the vector is not necessarily just a backing array pointer and some magic.

In contrast Go is really offering array syntax for this slice, that's the built-in array subscript operation and it cares whether v[3] exists when you try to compare it to 4.

[simiones]

I'm not sure I understand how this is relevant. In C++, arr[non_existent_index] is UB both if arr is an std::vector and if it is a C-style array. In Go it's a runtime error instead.

Sure, std::vector::operator[]() is not just syntax sugar for *(v+i), but I don't think any of this is relevant for the discussion at hand, unless I'm missing something.