http://d.puremagic.com/issues/show_bug.cgi?id=3556

           Summary: version(CTFE)
           Product: D
           Version: 1.050
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: cbkbbejeap@mailinator.com


--- Comment #0 from Nick Sabalausky <cbkbbejeap@mailinator.com> 2009-11-28 18:04:32 PST ---
Until CTFE includes all features of runtime and has 100% same semantics as runtime (and maybe even after then), there is often a need to have separate codepaths for ctfe and runtime. A version(CTFE) would be an improvement over the current solution of making alternate CTFE-intended functions and using a naming convention to distinguish.

version(CTFE)
{
    // Sacrifice speed, flexibility, or anything else
    // necessary to make this code work via CTFE.
}
else
{
    // Use proper D.
}

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--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-01-03 14:30:41 PST ---
Created an attachment (id=542)
Patch against DMD2 svn 324

Here is a patch which adds __ctfe as a 'magic variable'. It's a bool which is
true if evaluated in a function at compile-time, but false at run-time.
If evaluated outside a function, it gives a "non-constant expression" error.

Simple example:
---------
import std.stdio;

int foo() {
  if (__ctfe) return 3;
  writefln("run-time evaluated");
  return 2;
}

static assert(foo()==3);

void main()
{
  assert(foo()==2);
}
--------

The back-end throws out the if(__ctfe){...} part (even without optimisations
turned on), so there is no runtime penalty for adding if(__ctfe) clauses.

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com


--- Comment #2 from Walter Bright <bugzilla@digitalmars.com> 2010-01-11 22:05:10 PST ---
Changeset 332

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--- Comment #3 from Walter Bright <bugzilla@digitalmars.com> 2010-01-11 22:06:43 PST ---
The reason to prefer if(__ctfe) over version(CTFE) is that both code paths need
to be compiled properly, as a function could be executed both at compile and
runtime.

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Leandro Lucarella <llucax@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |llucax@gmail.com


--- Comment #4 from Leandro Lucarella <llucax@gmail.com> 2010-01-13 06:21:22 PST ---
Being that D2 is close to finalization, why do you keep introducing language identifiers starting with __. I think it's a very bad idea, as they are historically used for implementation specific features.

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Lars T. Kyllingstad <bugzilla@kyllingen.net> changed:

           What    |Removed                     |Added
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                 CC|                            |bugzilla@kyllingen.net


--- Comment #5 from Lars T. Kyllingstad <bugzilla@kyllingen.net> 2010-01-13 06:35:28 PST ---
How about

  if (meta.inCTFE) { ... }

for instance? (Assuming that __traits(xxx) becomes meta.xxx, of course.)

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--- Comment #6 from Don <clugdbug@yahoo.com.au> 2010-01-13 06:55:16 PST ---
(In reply to comment #4)
> Being that D2 is close to finalization, why do you keep introducing language identifiers starting with __. I think it's a very bad idea, as they are historically used for implementation specific features.

This *is* an implementation-specific feature. The user interface is not yet determined. Note that you can already write:
-----
module meta;

alias __ctfe  inCTFE;
-----

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Walter Bright <bugzilla@digitalmars.com> changed:

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


--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> 2010-01-30 22:45:33 PST ---
fixed dmd 2.040

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Stewart Gordon <smjg@iname.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg@iname.com


--- Comment #8 from Stewart Gordon <smjg@iname.com> 2010-01-31 06:16:49 PST ---
(In reply to comment #4)
> Being that D2 is close to finalization,

What are you talking about?  Not even D1 is finished yet, therefore what you say is impossible.

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