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digitalmars.D.bugs - [Issue 11648] New: rangeerror when adding element to associative array and value is implicitely converted by alias this

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11648

           Summary: rangeerror when adding element to associative array
                    and value is implicitely converted by alias this
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: r.sagitario gmx.de



PST ---
dmd 2.063 compiles and runs this code correctly:

//////////////////
import std.stdio;

struct S
{
    int _payload;
    alias _payload this;
}

void main()
{
    S[string] symbols;
    symbols["a"] = 1; // works if using S(1)
    writeln(symbols); // ["a":1]
}
////////////////

but dmd 2.064 causes a range error when executing:

core.exception.RangeError test(12): Range violation

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next sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11648


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

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





 dmd 2.063 compiles and runs this code correctly:
 
 //////////////////
 import std.stdio;
 
 struct S
 {
     int _payload;
     alias _payload this;
 }
 
 void main()
 {
     S[string] symbols;
     symbols["a"] = 1; // works if using S(1)
     writeln(symbols); // ["a":1]
 }
 ////////////////
 
 but dmd 2.064 causes a range error when executing:
 
 core.exception.RangeError test(12): Range violation


This is intended behavior introduce by fixing bug 6178.

Test case in compiler test suite.
https://github.com/D-Programming-Language/dmd/pull/2539/files#diff-a137107b45f82e7d3b516e2aff79f1d5R940

First, 'alias this' does not work for object construction.

struct S { int val; alias val this; }
S s = 1;   // compile error

And in your case, AA does not have a storage corresponding to the key "a" yet.
So, `symbols["a"] = 1;` should invoke _construction of S from integer 1_. But
as I shown, S cannot construct from int. So, compiler always treat the line as
_an assignment through alias this_. And of course, if the specified key does
not exist in AA, the indexing should throw RangeError.

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prev sibling parent d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11648




PST ---
Thanks for explanation.

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