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digitalmars.D.bugs - [Issue 11685] New: template opDispatch rejects-valid.

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=11685

           Summary: template opDispatch rejects-valid.
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: john.loughran.colvin gmail.com


--- Comment #0 from John Colvin <john.loughran.colvin gmail.com> 2013-12-04
22:05:46 GMT ---
this code:


template PartialApply(alias F, uint argLoc, Arg ...)
    if(Arg.length == 1)
{
    pragma(msg, "\nPartialApply!(", __traits(identifier, F),", ", argLoc, ", ",
Arg[0], ");\n"); 
    template PartialApply(L ...)
    {
        pragma(msg, "\nPartialApply!(", __traits(identifier, F),", ", argLoc,
", ", Arg[0], ").PartialApply!(", L, ");\n");
    alias PartialApply = F!(L[0 .. argLoc], Arg, L[argLoc .. $]);
    }
}

struct Pack(T...)
{
    template opDispatch(string s)
    {
        pragma(msg, "\n",typeof(this),".opDispatch!(\"",s,"\");\n");
    mixin("alias opDispatch = PartialApply!(." ~ s ~ ", 0, typeof(this));");
    }
}


struct asArg(T, uint argIndex)
{
    pragma(msg, "\n", typeof(this));
    pragma(msg, "asArg!(", T, ", ", argIndex, ");\n");
    template opDispatch(string s)
    {
        pragma(msg, "\n",typeof(this),".opDispatch!(\"", s, "\");\n");
    mixin("alias opDispatch = PartialApply!(." ~ s ~ ", " ~ argIndex.stringof ~
", T);");
    }
}

unittest
{
    pragma(msg, "\n" ,Pack!(1,2,3).asArg!(1).Pack!(0), "\n");
    alias A = Pack!(1,2,3).asArg!(1).Pack!(0);
}


produces this output:


$ dmd -unittest -c break.d


Pack!(1, 2, 3).opDispatch!("asArg");


PartialApply!(asArg, 0u, Pack!(1, 2, 3));


PartialApply!(asArg, 0u, Pack!(1, 2, 3)).PartialApply!(tuple(1));


F!(Pack!(1, 2, 3), 1)
asArg!(Pack!(1, 2, 3), 1u);


F!(Pack!(1, 2, 3), 1).opDispatch!("Pack");


PartialApply!(Pack, 1u, Pack!(1, 2, 3));


PartialApply!(Pack, 1u, Pack!(1, 2, 3)).PartialApply!(tuple(0));

F!(0, Pack!(1, 2, 3))

break.d(12): Error: struct break.Pack!(1, 2, 3).Pack template identifier
'asArg' is not a member of 'struct Pack'
break.d(12): Error: struct break.Pack!(1, 2, 3).Pack template identifier
'asArg' is not a member of 'struct Pack'



A few things jump out, other than the (hopefully) obvious rejects-valid:
1) The two lines 
    F!(Pack!(1, 2, 3), 1)
    asArg!(Pack!(1, 2, 3), 1u);
   should be the same. How can a struct not be able to work out it's own
typeof(this)?
2) There is an extra new-line at the top of the output and a missing new-line
between the last two pragma printouts.

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--- Comment #1 from John Colvin <john.loughran.colvin gmail.com> 2013-12-04
22:09:12 GMT ---
Also, note that it manages to print something halfway-correct for the unittest
pragma(msg, ...) even though it claims a much earlier error.


A clean version of the code without all the pragmas:

template PartialApply(alias F, uint argLoc, Arg ...)
    if(Arg.length == 1)
{
    template PartialApply(L ...)
    {
        alias PartialApply = F!(L[0 .. argLoc], Arg, L[argLoc .. $]);
    }
}

struct Pack(T...)
{
    template opDispatch(string s)
    {
        mixin("alias opDispatch = PartialApply!(." ~ s ~ ", 0,
typeof(this));");
    }
}


struct asArg(T, uint argIndex)
{
    template opDispatch(string s)
    {
        mixin("alias opDispatch = PartialApply!(." ~ s ~ ", " ~
argIndex.stringof ~ ", T);");
    }
}

unittest
{
    alias A = Pack!(1,2,3).asArg!(1).Pack!(0);
}

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--- Comment #2 from John Colvin <john.loughran.colvin gmail.com> 2014-01-15
10:20:11 GMT ---
An update:

The clean version above is now a simple rejects-valid.
If you place a pragma(msg, A); in the unittest then it prints the correct
thing, but the error saying "template identifier 'asArg' is not a member of
'struct Pack'" is still triggered.

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--- Comment #3 from John Colvin <john.loughran.colvin gmail.com> 2014-03-15
15:31:54 GMT ---
An even more reduced test-case:

template C(alias F)
{
    template C()
    {
        alias C = F;
    }
}

struct A
{
    template opDispatch(string s)
    {
    mixin("alias opDispatch = C!(." ~ s ~ ");");
    }
}

struct B
{
    enum blah = 42;
}

unittest
{
    alias Q = A.B!();
    pragma(msg, Q.blah);
}

$ rdmd -unittest break.d
break.d(9): Error: struct break.A template identifier 'B' is not a member of
'struct A'
break.d(9): Error: struct break.A template identifier 'B' is not a member of
'struct A'
42
Failed: ["dmd", "-unittest", "-v", "-o-", "break.d", "-I."]



As you can see, it knows the answer, but it is unnecessarily throwing an error.

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John Colvin <john.loughran.colvin gmail.com> changed:

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


--- Comment #4 from John Colvin <john.loughran.colvin gmail.com> 2014-03-15
16:47:01 GMT ---
*** This issue has been marked as a duplicate of issue 12373 ***

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