On 12/5/14 6:09 PM, Walter Bright wrote:
On 12/4/2014 1:32 PM, Steven Schveighoffer wrote:
On 12/4/14 3:58 PM, Walter Bright wrote:
On 12/4/2014 7:25 AM, Steven Schveighoffer wrote:
int* bar(scope int*);
scope int* foo();
bar(foo()); // Ok, lifetime(foo()) > lifetime(bar())
I'm trying to understand how foo can be implemented in any case. It
has no scope
ints to return, so where does it get the int from?
Could be from a global variable. Or a new'd value.
Well, OK, but why do that?
Why would a programmer do that? I often ask that question! But the
language allows it, therefore we must support it.
But you're the programmer that did it, it's YOUR example! :)
However, it's not just that, this is the ONLY example given as to why we
support scope returns. The language allows it, therefore we must support
it? But it's not allowed now, right? Why add it?
The scope return value does not affect what can be returned. It affects
how that return value can be used. I.e. the return value cannot be used
in such a way that it escapes the lifetime of the expression.
I assumed the scope return was so you could do things like:
scope int *foo(scope int *x)
{
return x;
}
which would be fine, I assume, right?
No. A scope parameter means the value does not escape the function. That
means you can't return it.
I think you should eliminate scope returns then. They are not useful. I
can't think of a single reason why a newly allocated via GC or global
reference return should have to be restricted to exist only within the
statement. Both have infinite lifetimes.
-Steve
