ref is unsafe

[Michel Fortin]

On 2012-12-30 22:29:33 +0000, Jonathan M Davis <jmdavisProg at gmx.com> said:

> Good point. Member variables of parameters also cause problems. So, it very
> quickly devolves to any function which accepts a user-defined type by ref and
> returns anything by ref would have to be @system, which is far from pleasant.

Note that the above definition includes every struct member function 
that returns a ref because of the implicit this parameter.

Also, it's not just functions returning by ref, it could be a function 
returning a delegate too, if the delegate happens to make use of the 
reference:

void delegate() foo(ref int a) {
    return { writeln(a); };
}

void delegate() bar() {
    int a;
    return foo(a); // leaking reference to a beyond bar's scope
}

And similar to passing a value by ref: you can pass a slice to a static 
array, then return the slice:

int[] foo(int[] a) {
	return a;
}

int[] bar() {
	int[2] a;
	return foo(a[]);
}

Three variations on the same theme.

-- 
Michel Fortin
michel.fortin at michelf.ca
http://michelf.ca/