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digitalmars.D.bugs - [Issue 9563] New: (2.062) typeof(T[0]) no longer works with array T's

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9563

           Summary: (2.062) typeof(T[0]) no longer works with array T's
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: siegelords_abode yahoo.com



Both invocations of ElemTypeOf used to work fine with DMD 2.061 but with DMD
2.062 only the class one works. Either none of them should work, or preferably
both should work as they had since D1:

template ElemTypeOf( T )
{
    alias typeof(T[0]) ElemTypeOf;
}

class A
{
    int opIndex(size_t i)
    {
        return 0;
    }
}

void main()
{
    ElemTypeOf!(A) a;
    ElemTypeOf!(int[]) b;

    static assert(is(typeof(a) == int));
    static assert(is(typeof(b) == int));
}

With dmd 2.062 the second invocation now gives the error:

test.d(3): Error: argument int[][0LU] to typeof is not an expression
test.d(3): Error: argument int[][0LU] to typeof is not an expression
test.d(17): Error: template instance test.ElemTypeOf!(int[]) error
instantiating
test.d(20): Error: static assert  (is(_error_ == int)) is false

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Feb 21 2013
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9563


Marco Leise <Marco.Leise gmx.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Marco.Leise gmx.de



You made me smile. I recently needed ElementType! in my code for arrays. I had
almost written a simple template, but remembered that Phobos had it already.
And I thought "I better use the Phobos one, that's sure to still work in the
future. Not that it's likely that typeof(T[0]) breaks anytime soon... but
still." Sometimes you have these gut feelings you can't even explain to
co-workers.

Sorry for the noise.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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monarchdodra gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |monarchdodra gmail.com





 Both invocations of ElemTypeOf used to work fine with DMD 2.061 but with DMD
 2.062 only the class one works. Either none of them should work, or preferably
 both should work as they had since D1:


What do you mean "only the class one works"? I'm getting a failure for both
asserts.

Furthermore, I expect a failure. Your ElemTypeOf simply declares a static array
of size 0 of your type, it is not actually calling opIndex. Then combining it
with calling "typeof" on something that is already a type, makes this dobly
wrong code.

This worked in 2.060, but was fixed starting in 2.061.

Try something like this:

template ElemTypeOf( T )
{
    static private T t = T.init;
    alias typeof(t[0]) ElemTypeOf;
}

Or better yet, std.range's ElementType or ElementEncodingType.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 What do you mean "only the class one works"? I'm getting a failure for both
 asserts.


I am not with DMD 2.062. This code compiles without any error and prints "int":

template ElemTypeOf( T )
{
    alias typeof(T[0]) ElemTypeOf;
}

class A
{
    int opIndex(size_t i)
    {
        return 0;
    }
}

void main()
{
    ElemTypeOf!(A) a;

    pragma(msg, typeof(a).stringof);
    static assert(is(typeof(a) == int));
}


 This worked in 2.060, but was fixed starting in 2.061.
 
 Try something like this:
 
 template ElemTypeOf( T )
 {
     static private T t = T.init;
     alias typeof(t[0]) ElemTypeOf;
 }


I guess that works (with some simplification of course), although the existence
of a workaround does not negate the existence of the regression.


 Or better yet, std.range's ElementType or ElementEncodingType.


Not using Phobos.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 What do you mean "only the class one works"? I'm getting a failure for both
 asserts.


 
 I am not with DMD 2.062. This code compiles without any error and prints "int":
 

 This worked in 2.060, but was fixed starting in 2.061.




My bad, I must have botched the test. That does indeed work in 2.061, so was
broken in 2.062.


 Try something like this:
 
 template ElemTypeOf( T )
 {
     static private T t = T.init;
     alias typeof(t[0]) ElemTypeOf;
 }


 
 I guess that works (with some simplification of course), although the existence
 of a workaround does not negate the existence of the regression.


Well, as I said, I think this is not a matter of regression and workaround, but
rather wrong code finally getting rejected, and new and correct code being
deployed to replace it.

In any case, I'll let one of the more compiler knowledgeable guys (Kenji?
Walter) give you definitive answer.

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Feb 22 2013
prev sibling parent d-bugmail puremagic.com writes:
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Steven Schveighoffer <schveiguy yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |schveiguy yahoo.com
         Resolution|                            |INVALID



08:21:07 PST ---
This is indeed a bug that was fixed.

T[0] is applying index to the type, not an instance of the type.  I wouldn't
expect typeof(T[0]) to work at all, it's like saying typeof(int) (which doesn't
compile), typeof converts an expression into its type.

You should be able to do typeof(T.init[0]).

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