http://d.puremagic.com/issues/show_bug.cgi?id=4001

           Summary: ctfe return value is handled incorrectly when used as
                    template argument
           Product: D
           Version: 2.041
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: jelszonak@gmail.com


--- Comment #0 from Zólyomi István <jelszonak@gmail.com> 2010-03-24 00:59:45 PDT ---
Note that the dmd version I was working with was 2.042, but it was still unavailable in the version list. The reduced test case is the following:

import std.metastrings;

// dummy ctfe-capable function needed to reproduce the error long parseLong(string timeStr) { return 42; }

// ctfe-capable function to demonstrate that a value is calculated in
compile-time
string longToStr(long val)
{
    if (val < 10) { return "" ~ cast(char)(val + '0'); }
    else { return longToStr(val / 10) ~ longToStr(val % 10); }
}

void main(string[] args)
{
    const long mylong = parseLong("mystring");
    pragma(msg, "fine ", longToStr(mylong) ); // compiles and prints
    pragma(msg, "bug? ", std.metastrings.toStringNow!(mylong) ); // error
}

For this code, the compiler output is

fine 42
bug? c:\Program Files\.....\src\phobos\std\metastrings.d(97): Error: expression
mylong < 0L is not constant or does not evaluate to a bool

I think this is a bug, toStringNow should work just as like longToStr. I checked its source code, but found no reason for the compile error, it seems to do the same thing with templates as longToStr with ctfe. The bug was confirmed on the newsgroups, see thread starting with

http://digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=107973

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

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


--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-03-24 01:28:46 PDT ---
This isn't actually a CTFE problem. The issue is that constant folding isn't being performed on const variables with initializers. BTW in the original bug, you can replace 'const' with 'enum' and it will work fine. Note that const variables are NOT evaluated at compile time. But in these kind of situations, it should do the same thing it does with a CTFE function call.

Reduced test case:
----
int space() { return 4001; }

void oddity4001()
{
    const int bowie = space();
    static assert(space() == 4001); // OK
    static assert(bowie == 4001);   // doesn't compile
}

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Steven Schveighoffer <schveiguy@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schveiguy@yahoo.com


--- Comment #2 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-03-24 11:29:52 PDT ---
(In reply to comment #1)
< Note that const
> variables are NOT evaluated at compile time. But in these kind of situations, it should do the same thing it does with a CTFE function call.

Then how does the first pragma work?  It uses the same const variable that supposedly isn't evaluatable at compile time in the second pragma...

-Steve

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--- Comment #3 from Don <clugdbug@yahoo.com.au> 2010-03-24 11:58:27 PDT ---
(In reply to comment #2)
> (In reply to comment #1)
> < Note that const
> > variables are NOT evaluated at compile time. But in these kind of situations, it should do the same thing it does with a CTFE function call.
> 
> Then how does the first pragma work?  It uses the same const variable that supposedly isn't evaluatable at compile time in the second pragma...
> 
> -Steve

I didn't express that very clearly. Const variables are not evaluated at instantiation. It is permitted for a const variable to be determined at runtime.

If a CTFE function call is made, all the arguments are interpreted before calling the function. In the test case, it only becomes a compile-time value while evaluating the pragma. (The pragma is forcing it to be a compile-time value).

The bug is that this constant folding is not happening in template instantiations, static assert, static if, etc.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|ctfe return value is        |const variables should be
                   |handled incorrectly when    |readable inside CTFE
                   |used as template argument   |


--- Comment #4 from Don <clugdbug@yahoo.com.au> 2011-04-26 21:10:03 PDT ---
Original title:
ctfe return value is handled incorrectly when used as template argument

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Walter Bright <bugzilla@digitalmars.com> changed:

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


--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> 2011-04-27 20:07:11 PDT ---
https://github.com/D-Programming-Language/dmd/commit/97c73b140f1cde5d0b713eb72fd1e82084a6ac11

https://github.com/D-Programming-Language/dmd/commit/13dcf90d934325b4f37c50679e07978a821c4249

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