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digitalmars.D.bugs - [Issue 4001] New: ctfe return value is handled incorrectly when used as template argument

reply d-bugmail puremagic.com writes:
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



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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Mar 24 2010
next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

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



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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Steven Schveighoffer <schveiguy yahoo.com> changed:

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



11:29:52 PDT ---

< 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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 < 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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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4001


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   |



Original title:
ctfe return value is handled incorrectly when used as template argument

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Apr 26 2011
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4001


Walter Bright <bugzilla digitalmars.com> changed:

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



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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Apr 27 2011