🚀 go-pugleaf

In article <1992Oct31.025229.6520@cs.brown.edu> sdm@cs.brown.edu (Scott Meyers) writes:

> Is the return type of operator= an lvalue?  In particular, if a, b, and c
> are of built-in type, is this legal?

>     (a = b) = c;

Yes.

> My goal is to determine the correct type for user-defined operator=.  If
> the return type is to be an lvalue, then for a class C, the return type
> should be C&.

It should be C&.  The general rule is that any built-in operator that
returns one of its operands will do so as an lvalue if the operand is.
(except ?:, which yields an lvalue only if both the alternatives are
lvalues of the same type).

The thing that motivated this decision was a member function like this:

	T& T::fun() {
		// ...
		return (*this = /*some value*/);
	}

The person who wrote this thought that

	return (*this = /*some value*/);

would mean the same as

	*this = /*some value*/;
	return *this;

but in a function that returns a T&, it means the same only if = yields a T&.

This is a strict extension from C: there is no way to write a strictly
conforming C program that is capable of detecting whether = returns an
lvalue.
-- 
				--Andrew Koenig
				  ark@europa.att.com