Thread overview
[Issue 17729] dmd says cast expression is "not an lvalue", but it can be used as one in other contexts
Sep 19, 2018
er.krali@gmail.com
Sep 19, 2018
ag0aep6g
Sep 19, 2018
er.krali@gmail.com
Mar 19, 2019
ag0aep6g
May 25, 2019
ag0aep6g
September 19, 2018
https://issues.dlang.org/show_bug.cgi?id=17729

er.krali@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |er.krali@gmail.com

--- Comment #1 from er.krali@gmail.com ---
Furthermore, it doesn't work with ref parameters either:

---
struct S {
    int i;
}

void fun(ref S s, int i) {
    s.i = i;
}

void main() {
    shared S s;

    /* This fails:

       onlineapp.d(17): Error: function onlineapp.fun(ref S s, int i) is not
callable using argument types (S, int)
       onlineapp.d(17):        cannot pass rvalue argument cast(S)s of type S
to parameter ref S s

    fun(cast(S) s, 1);

    */

    (*(cast (S*) &s)).fun(1); // Nasty workaround
    assert (s.i == 1);
}
---

I also can't understand why the workaround works at all, the result of dereferencing a pointer should surely be a rvalue?

Is that also a bug?

--
September 19, 2018
https://issues.dlang.org/show_bug.cgi?id=17729

--- Comment #2 from ag0aep6g <ag0aep6g@gmail.com> ---
(In reply to er.krali from comment #1)
> I also can't understand why the workaround works at all, the result of dereferencing a pointer should surely be a rvalue?
> 
> Is that also a bug?

Dereferencing a pointer gives an lvalue. If it gave an rvalue, pointers would be pretty useless. You couldn't assign through them.

If you disagree or have more questions on this, I'd suggest making a thread on D.learn [1]. We're going off topic here.


[1] https://forum.dlang.org/group/learn

--
September 19, 2018
https://issues.dlang.org/show_bug.cgi?id=17729

--- Comment #3 from er.krali@gmail.com ---
(In reply to ag0aep6g from comment #2)
> Dereferencing a pointer gives an lvalue. If it gave an rvalue, pointers would be pretty useless. You couldn't assign through them.
> 
> If you disagree or have more questions on this, I'd suggest making a thread on D.learn [1]. We're going off topic here.
> 
> 
> [1] https://forum.dlang.org/group/learn

Sure, now that I think about it, it seems indeed obvious, sorry for the OT.

--
March 19, 2019
https://issues.dlang.org/show_bug.cgi?id=17729

ag0aep6g <ag0aep6g@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=19754

--
March 26, 2019
https://issues.dlang.org/show_bug.cgi?id=17729

Andrei Alexandrescu <andrei@erdani.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrei@erdani.com
           Assignee|nobody@puremagic.com        |razvan.nitu1305@gmail.com

--
May 25, 2019
https://issues.dlang.org/show_bug.cgi?id=17729

ag0aep6g <ag0aep6g@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #4 from ag0aep6g <ag0aep6g@gmail.com> ---
This has apparently been fixed by the fix for issue 19754. `auto p = & cast(S) s;` compiles now. Closing as duplicate.

*** This issue has been marked as a duplicate of issue 19754 ***

--