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digitalmars.D.bugs - [Issue 7046] New: CTFE: append null does nothing

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7046

           Summary: CTFE: append null does nothing
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: destructionator gmail.com



18:07:38 PST ---
string[] test() {
    string[] ret;

    ret ~= null;
    ret ~= null;

    assert(ret.length == 2); // fails
    return ret;
}

void main() {
    enum ctfe = test();
}

===
test90.d(7): Error: assert(ret.length == 2u) failed
test90.d(12):        called from here: a()

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next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au



This works on git HEAD. Probably a duplicate of a recently fixed bug.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Steven Schveighoffer <schveiguy yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schveiguy yahoo.com



04:30:34 PST ---
Are we sure this isn't expected?  I mean a null could mean a null string[], not
a null string.

string[] ret;
string[] a = null;

ret ~= a;
ret ~= a;

neither of these lines should do anything to ret, since they are empty arrays
of the same type.

I almost think the code in question should fail to compile for being too
ambiguous.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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See bug 2006.

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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc






 I almost think the code in question should fail to compile for being too
 ambiguous.


Right.

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04:54:29 PST ---


 See bug 2006.


So is this a dupe?  I'm concerned there was a change in git that makes this
"work."  Moving from one ambiguous interpretation to another doesn't sound like
progress.

Do we have some definitive answer on what *should* happen?

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07:47:17 PST ---


 I mean a null could mean a null string[], not a null string.


I oversimplified the test - in the original code it came from,
it was more like

string a = null;
ret ~= a;

which gets the same result in 2.056

I haven't tried git though. I'm not sure how to use that yet!


 I almost think the code in question should fail to compile for being too
 ambiguous.


With null itself... maybe. In the case of string[], ~= null could
have two meanings, but one of them is pretty obviously a no-op, so it's
probably not what you meant.

If a variable happens to be null, maybe doing nothing is what you wanted,
but in that case, the variable has an exact type declared so it's not
ambiguous anymore.

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07:53:36 PST ---
BTW, I labeled this as CTFE because in 2.056, running the same function at
runtime, the assert passes.

I think this worked in CTFE a couple releases ago too, and since it works in
the git version again, it was probably just a temporary regression in the
interpreter.

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Don <clugdbug yahoo.com.au> changed:

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



This compiled on DMD2.053, but generated wrong code. It failed to compile on
2.054 to 2.056. Fixed 2.057 -- dup of bug 6077

*** This issue has been marked as a duplicate of issue 6077 ***

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Dec 14 2011