[Issue 18282] [Scope][DIP1000]Assignment of local variable to `scope` variable not recognized by compiler

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18282

ag0aep6g at gmail.com changed:

           What    |Removed                     |Added
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                 CC|                            |ag0aep6g at gmail.com

--- Comment #2 from ag0aep6g at gmail.com ---
(In reply to Walter Bright from comment #1)
> (In reply to Mike Franklin from comment #0)
> > void main() @safe
> > {
> >     string foo = "foo";
> >     scope string*[] ls;
> >     ls ~= &foo;
> > }
> > 
> > Compile with `-dip1000`
> > 
> > onlineapp.d(5): Error: reference to local variable foo assigned to non-scope
> > ls
> 
> While ls is scope, ls[] is not scope. Scope is not transitive, hence the
> compiler error.

I assume that you don't mean `ls[]` literally, but rather that the elements of
`ls` aren't `scope`, right?

That means, it should be okay to return `ls[0]` because that's not `scope`,
right? But that doesn't work:

----
string* f() @safe
{
    scope string*[] ls;
    return ls[0]; /* Error: scope variable ls may not be returned */
}
----

On the other hand, this works:

----
void main() @safe
{
    string foo = "foo";
    scope string*[] ls;
    ls = ls ~ &foo;
}
----

The only difference from the original code is `ls ~= &foo;` -> `ls = ls ~
&foo;`. Those two assignments should be equivalent [1], no? Either both should
be accepted, or both should be rejected.


[1] https://dlang.org/spec/expression.html#assignment_operator_expressions

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