http://d.puremagic.com/issues/show_bug.cgi?id=3608

           Summary: Allow isExpression and templates to capture template
                    parameters and FQN of template
           Product: D
           Version: future
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: simen.kjaras@gmail.com


--- Comment #0 from Simen Kjaeraas <simen.kjaras@gmail.com> 2009-12-11 07:26:57 PST ---
Currently, there is no way to extract FQN of a template from an instantiation, nor to get its parameters. This is not completely true, as one could parse its stringof representation, but this is often not enough.

I therefore propose that the following syntax be allowed:

template foo( T : U!( V ), U, V... )

Thus, one could get the base template or parameters of an instantiation using the following templates:

template BaseTemplate( T : U!( V ), U, V... ) {
  alias U BaseTemplate;
}
template TemplateParameters( T : U!( V ), U, V... ) {
  alias V TemplateParameters;
}

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Simen Kjaeraas <simen.kjaras@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|future                      |D2
           Severity|enhancement                 |normal


--- Comment #1 from Simen Kjaeraas <simen.kjaras@gmail.com> 2010-11-08 05:21:14 PST ---
Judging by the recent resolution of bug 1714, this is not so much an enhancement as a planned feature. Updating the syntax:

template foo( T : U!V, alias U, V... ) {
    //...
}

template BaseTemplate( T : U!( V ), alias U, V... ) {
    alias U BaseTemplate;
}
template TemplateParameters( T : U!( V ), alias U, V... ) {
    alias V TemplateParameters;
}

This may be a separate bug, as it concerns variadic parameter lists, something bug 1714 fails to take into account.

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Don <clugdbug@yahoo.com.au> changed:

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


--- Comment #2 from Don <clugdbug@yahoo.com.au> 2010-11-08 06:22:55 PST ---
The patch in bug 5614 fixes some issues which seem similar to these.
But I'm not sure what these test cases are supposed to do. It seems to be an
attempt to use IFTI, but note that IFTI only applies to function templates. But
type deduction can also be used in is() expressions.

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--- Comment #3 from Simen Kjaeraas <simen.kjaras@gmail.com> 2010-11-08 07:00:15 PST ---
I'm not sure what it is that confuses you. D allows constraints to be placed on template parameters not only by means of template constraints, but also isExpression-like patterns in the parameter list:

class A {}
class B : A {}

template isAnA( T : A ) {
    enum isAnA = true;
}

static assert( isAnA!B );

This also works for more complex type constraints:

template extractTupleArgs( T == Tuple!U, U... ) {
    alias U extractTupleArgs;
}

static assert( is( extractTupleArgs!( Tuple!int ) == int ) );

It does however not work for complex type constraints where the template is not known:

template dissectTemplate( T == U!V, V... ) {
    alias U tmpl;
    alias V args;
}

And it is this last case I want covered.

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--- Comment #4 from Simen Kjaeraas <simen.kjaras@gmail.com> 2010-11-08 07:02:15 PST ---
(In reply to comment #3)
> template dissectTemplate( T == U!V, V... ) {


This should of course be

template dissectTemplate( T == U!V, alias U, V... ) {

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull, rejects-valid


--- Comment #5 from Kenji Hara <k.hara.pg@gmail.com> 2012-05-20 09:51:48 PDT ---
https://github.com/D-Programming-Language/dmd/pull/958

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--- Comment #6 from github-bugzilla@puremagic.com 2012-05-20 12:48:06 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/b327dd61e685c85adfdceef0767b4a456350667b
fix Issue 3608 - Allow isExpression and templates to capture template
parameters and FQN of template

https://github.com/D-Programming-Language/dmd/commit/ed68238cd1e5a7aec454840ee11e04580f974855 Merge pull request #958 from 9rnsr/fix_tided

Issue 1780 & 3608 & 8125 - Fix TypeInstance deduction problems

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla@digitalmars.com
         Resolution|                            |FIXED


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