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digitalmars.D.bugs - [Issue 3608] New: Allow isExpression and templates to capture template parameters and FQN of template

reply d-bugmail puremagic.com writes:
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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next sibling parent d-bugmail puremagic.com writes:
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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... ) { -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Nov 08 2010