[SOLVED] Does the type information of an object also take up space in memory?

Does the type information of an object also take up space in memory?

I'm trying to understand how type information is stored in memory.

We often say that an 8-bit value can store 2⁸ = 256 different values. But I'm wondering — when we create an object of that type, doesn't the information about the type itself (e.g., "this is an integer") also occupy space in memory?

In other words, if I have an 8-bit object, are only 8 bits used in memory? Or is additional memory used to store the object's type metadata? How does this differ between low-level languages (like C or C++) and high-level languages (like Python or JavaScript)?

Solution

This information isn't stored at runtime (except for polymorphic types, i.e. the classes with virtual functions; for those look up "RTTI" and "vtables").

It is baked into the generated instructions. E.g. for:

void foo(int &x)
{
    x += 42;
}

On the assembly level the function just receives a pointer, and x += 42; compiles to "assume that the pointer points to an int, and add 42 to it".

The code trusts that the pointer it receives actually points to an object of that type.

This is all for C/C++, of course. Interpreted languages like Python have to store the type information at runtime.