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digitalmars.D.bugs - [Issue 8364] New: Allow exclamation mark in template definition

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8364

           Summary: Allow exclamation mark in template definition
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: qwertie256 gmail.com


--- Comment #0 from David Piepgrass <qwertie256 gmail.com> 2012-07-09 13:12:42
PDT ---
The syntax of templates should be similar at the definition as it is at the
call site:

T sum!(T,R)(R range) if (isInputRange!R...) { ... }

Of course, the existing syntax must be kept too.

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next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

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--- Comment #1 from bearophile_hugs eml.cc 2012-07-09 13:17:24 PDT ---
(In reply to comment #0)

 The syntax of templates should be similar at the definition as it is at the
 call site:


Why?

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Jonathan M Davis <jmdavisProg gmx.com> changed:

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--- Comment #2 from Jonathan M Davis <jmdavisProg gmx.com> 2012-07-09 13:25:16
PDT ---
Of what value is that? The current situation is wonderfully unambiguous.

This proposal would make the parser's life harder and would probably make it so
that the grammar could no longer be context free (which would be very bad). And
from the perspective of the programmer (not just the compiler), it's _useful_
to be able to tell the difference between a template and a template
instantiation at a glance.

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timon.gehr gmx.ch changed:

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--- Comment #3 from timon.gehr gmx.ch 2012-07-09 13:36:26 PDT ---
(In reply to comment #2)

 Of what value is that? The current situation is wonderfully unambiguous.
 


True.


 This proposal would make the parser's life harder


Not really. Having this as the only template declaration syntax would even make 
the parser's life easier. (and if both were legal, parsing the kind that has 
the '!' would be slighly more efficient.)


 and would probably make it so that the grammar could no longer be context free 


This is not the case. The grammar would stay context free.


 (which would be very bad).
 And from the perspective of the programmer (not just the compiler), it's 
 _useful_ to be able to tell the difference between a template and a template
 instantiation at a glance.


The proposal does not put this ability in danger.

Anyway, I don't prefer either scheme and in my opinion it is fine to either 
leave the template declaration grammar as it is, or to change it to always
require '!'. The latter is not going to happen though.

(I remember that when I wrote my very first function template in D, I 
used the proposed syntax and was confused that it didn't work.)

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--- Comment #4 from David Piepgrass <qwertie256 gmail.com> 2012-07-10 12:31:37
PDT ---

 Why?


Because one syntax is easier to learn than two. Timon said "when I wrote my
very first function template in D, I used the proposed syntax and was confused
that it didn't work", and that makes two of us (well, I quickly realized why
the compiler complained, but my first instinct is to use !, and it feels really
dumb that I can't).

Plus, the parser might be able to handle ! more quickly, since it will know to
expect "TemplateParameterList" instead of "Parameters".

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