• d-bugmail puremagic.com Jul 03 2008
• d-bugmail puremagic.com Jul 04 2008
• d-bugmail puremagic.com Jul 04 2008
• d-bugmail puremagic.com Jul 09 2009

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2192

           Summary: Returning element in an AA of AAs during nested foreach
                    generates compiler error
           Product: D
           Version: 1.029
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: business3 twistedpairgaming.com


The following code generates a rather curious compiler error:

BEGIN CODE
class Foo { }
Foo[char][char] jaggedArray;

Foo Bar()
{
        foreach(Foo[char] array; jaggedArray)
        {
                foreach(Foo f; array)
                {
                        return null; // Error
                }
        }
}
END CODE

Compiler output from both DMD 1.029 and DMD 1.031:
testb1.d(10): Error: cannot implicitly convert expression (null) of type void*
to int
testb1.d(10): Error: cannot implicitly convert expression (cast(int)null) of
type int to testb1.Foo

Changes that DO NOT eliminate the error:
- Changing "jaggedArray" to "Foo[char[]][char[]]"
- Adding "return null;" to the end of the function
- Changing "return null;" to "return f;"

That last change (returning "f" instead of "null") generates the following
error:
testb1.d(10): Error: cannot implicitly convert expression (f) of type
testb1.Foo to int
testb1.d(10): Error: cannot implicitly convert expression (cast(int)f) of type
int to testb1.Foo

So, that means: The function Bar() is declared to return a Foo, and it tries to
return a Foo. But the compiler tries to turn the Foo into an int...and then
back into a Foo again.

Changes that DO cause the code to compile:
- Changing "jaggedArray" to any of the following: "Foo[][char]" "Foo[char][]"
"int[char][char]"
- Eliminating the inner foreach
- Eliminating the outer foreach and iterating over "jaggedAray['a']"

The following change also causes the code to compile:

class Foo { int var; }
Foo[char][char] jaggedArray;

Foo Bar()
{
        foreach(Foo[char] array; jaggedArray)
        {
                foreach(Foo f; array)
                {
                        f.var = 5;
                }
        }

        return null;
}


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2192





------- Comment #1 from business3 twistedpairgaming.com  2008-07-04 02:22
-------
Changing the function's return type to something else, like 'bool' also
eliminates the problem.

Making the return statement conditional (ex "if(f.var == 1) return null;") does
NOT solve to problem.

If you need to return f, the following workaround does work (although it will
result in extra unnecessary iterations):

Foo Bar()
{
        Foo ret = null;
        foreach(Foo[char] array; jaggedArray)
        {
                foreach(Foo f; array)
                {
                        if( /* whatever you need */ )
                        {
                                if(ret == null)
                                        ret = f;
                                break;
                        }
                }
        }
        return ret;
}


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2192





------- Comment #2 from business3 twistedpairgaming.com  2008-07-04 02:25
-------
Erm...that should be "is null" in the workaround, not "== null". Must be
tired...


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2192





--- Comment #3 from Serg Kovrov <kovrov+puremagic gmail.com>  2009-07-09
07:55:32 PDT ---
Same error is issued on returning from nested foreach over opApply/delegates.

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