Reference to value

Question

I have an issue concerning the way references behave in rust : I made an example to show my misunderstanding, of course there is a much simpler version of the function, this is not the point, the point is the behaviour of references in Rust.

Consider these five following functions :

This code compile perfectly

fn add2(parameter : &isize) -> isize {
    let a : isize = parameter + 2;
    a
}

This code don't compile : mismatched type, expected isize, found &isize

fn add2(parameter : &isize) -> isize {
    let a : isize = parameter;
    a + 2
}

This code don't compile either : casting &isize as isize is invalid cannot cast &isize as isize (well, I expected it here)

fn add2(parameter : &isize) -> isize {
    let a : isize = parameter as isize;
    a + 2
}

This code compile

fn add2(parameter : &isize) -> isize {
    let a : isize = *parameter;
    a + 2
}

And finally, this code compile too

fn add2(parameter : &isize) -> isize {
    let a : isize = *parameter + 2;
    a
}

So my questions are :

• Why is the first one compiling if the second one does not ? (operator+ overload for references ?)
• Why auto-dereference mecanism doesn't work on the second one ? (and on the third one)