Re: What on earth is a ref function?

[Simen kjaeraas]

simendsjo <simen.end...@pandavre.com> wrote:

The spec is very short here, and the example doesn't give me much..

// I thought "allows functinos to return by reference" meant it could return local variables..

ref int* ptr() {
        auto p = new int;
        *p = 12;
        return p; // Error: escaping local variable
}

This fails because p itself is stack allocated. By reference means it
returns a hidden pointer to something. Because this is a pointer, you
can get the address of the returned value, and do things to it.

// So whats the difference between these functions?

ref int val() {
        auto p = new int;
        assert(*p == 0);
        *p = 10;
        assert(*p == 10);
        return *p;
}

This returns what is in effect p - a pointer (reference) to an int.

int val2() {
        auto p = new int;
        *p = 10;
        return *p;
}

This returns simply the value of *p.

unittest
{
        assert(val() == 10);
        assert(val2() == 10);
        auto retvalue = val() = 99; // References can be lvalues.. What?
        assert(retvalue == 99);
}

Giving an example of what one can do with a reference:

ref int foo( ref int val ) {
    return ++value;
}

int n = 3;
foo( n ) = 4;
assert( n == 4 );
assert( foo( n ) == 5 );

--
Simen