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digitalmars.D.bugs - [Issue 11857] New: `out` parameter breaks overload resolution

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11857

           Summary: `out` parameter breaks overload resolution
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: ice, rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: verylonglogin.reg gmail.com



17:00:51 MSK ---
This code should compile:
---
void f(int) { }
void f(out int) { }
void t(T)(T) { }
void t(T)(out T) if(false) { } // line 4

void main()
{
    const int n = 1;
    f(n); // line 9
    t(n); // also causes ICE
}
---
main.d(9): Error: constant 1 is not an lvalue
main.d(4): Error: cannot have const out parameter of type const(int)
<access violation>
---

Previously dmd just shown error. Now it also ICE-s with access violation in
template case.

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Jan 02 2014
next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11857


Kenji Hara <k.hara.pg gmail.com> changed:

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



https://github.com/D-Programming-Language/dmd/pull/3034

*** This issue has been marked as a duplicate of issue 11822 ***

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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11:07:39 MSK ---


 https://github.com/D-Programming-Language/dmd/pull/3034
 
 *** This issue has been marked as a duplicate of issue 11822 ***


If it really is change issue 11822 title appropriately as this issue has
nothing to do with `-de` switch.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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01:53:22 MSK ---
So do I understand correctly ICE part of the issue is considered a duplicate of
issue 11822 and "This code should compile" part is considered WONTFIX? If so,
where is the documentation claiming such code incorrect?

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Jan 11 2014
prev sibling next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11857






 So do I understand correctly ICE part of the issue is considered a duplicate of
 issue 11822 and "This code should compile" part is considered WONTFIX? If so,
 where is the documentation claiming such code incorrect?


In short, yes.

Even `const int n = 1` is interpreted in compile time, `n` is a local variable
that has runtime storage on stack. Therefore, expression `n` makes lvalue, then
preferentially matches to `out` parameter.


This behavior is intended to reduce confusion at the situation that mixing
constant-folding and compile-time/runtime evaluation. Example:

void f(    immutable int n);
void f(ref immutable int n);  // accepts only lvalue

void foo(int x)
{
    immutable int n = x;
            // n is evaluated in runtime (when foo is called)
    f(n);   // n matches to ref version
}
void bar(int x)
{
    immutable int n = 1;
            // n can be interpreted at compile time,
            // but still allocated on stack and initialized in runtime.
    f(n);   // n still matches to ref version
}

D is designed to provide consistent overload resolution result for f(n) in both
foo and bar.
In other words, variable evaluation and its ref-ness is strictly separated from
the CTFE/constant-folding. Conflating them would make hard to understand
overload resolution result.

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Jan 13 2014
prev sibling next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11857




18:28:07 MSK ---


Thanks, but this doesn't answer the question. Probably I should be more
precise:
1. Why `ref` works and `out` doesn't work (in `ref` case the only matching
non-ref overload is selected)?
2. Why disabled by `if(false)` constraint overload breaks overload resolution?

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18:57:38 MSK ---
I segregated Issue 11915 and Issue 11916 for discussion.

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