• via Digitalmars-d-bugs (62/62) Apr 24 2017 https://issues.dlang.org/show_bug.cgi?id=17346

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=17346

          Issue ID: 17346
           Summary: Inconsistent l/rvalue overload resolution
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: petar.p.kirov gmail.com

As Steven mentioned in this forum post [1], given an overload that varies
solely on ref, then rvalue arguments should go to the non-ref and lvalue
arguments should go to the ref. A simple test indicates that the above rule is
true, but only if the ref overload is non-const:

struct X { int x; }

struct Y1
{
    this(X x)
    {
        writeln("rvalue: ", x.x);
    }

    this(const ref X x) // const
    {
        writeln("const lvalue ref: ", x.x);
    }
}

struct Y2
{
    this(X x)
    {
        writeln("rvalue: ", x.x);
    }

    this(ref X x) // non-const
    {
        writeln("lvalue ref: ", x.x);
    }
}

import std.stdio;

void main()
{
    auto y1_rval = Y1(X(1));
    auto x1_lval = X(2);
    auto y1_lval = Y1(x1_lval); // should call the ref-overload

    auto y2_rval = Y2(X(3));
    auto x2_lval = X(4);
    auto y2_lval = Y2(x2_lval); // should call the ref-overload
}

Expected output:
Rvalue: 1
const lvalue ref: 2
Rvalue: 3
Lvalue ref: 4

Actual output:
Rvalue: 1
Rvalue: 2
Rvalue: 3
Lvalue ref: 4

[1]: http://forum.dlang.org/post/odl0e1$1qkq$1 digitalmars.com

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