[Issue 10138] Regression (2.063 git-head): Using ReturnType with scoped no longer works

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10138



--- Comment #5 from Kenji Hara <k.hara.pg at gmail.com> 2013-05-27 15:39:22 PDT ---
(In reply to comment #4)
> Here's the thing, though. In that phobos pull, monarchdodra commented with:
> 
> "Finally, I gave Scoped an @disabled this() to prevent our smarter users from
> trying to build a Scoped using typeof."
> 
> It seems like he is actively trying to *disallow* using either ReturnType or
> typeof in order to create a scoped field variable.
> 
> But, typeof still works. In 2.063 your example code will become:
[snip]

You are confusing about @disable for `Scoped` struct default construction and
calling `scoped` function with zero argument.

If new A() is valid, scoped!A() is also valid. The latter is corresponding to
the former. It's the design of scoped utility.

> So now I can't tell whether we *support* using scoped field variables or is the
> above just a hack? I need to know what to put in the changelog.

The rejected case from 2.063 is this:

class A
{
    this() {}
    this(int) {}
}

class B
{
    typeof(scoped!A()) a;

    this()  // L12
    {
        //a = scoped!A();
        //a = scoped!A(1);
    }
}

Output:
test.d(12): Error: constructor test.B.this field a must be initialized in
constructor

The field B.a is must be initialized in constructor, comes from the @disable
this() defined in typeof(scoped!A()) struct.

However, getting the type of Scoped struct by using typeof is still allowed. So

typeof(scoped!A()) a;

is valid from 2.063.

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