• Bobby Bingham (20/20) Aug 20 2012 I'm just getting started with D, and was playing around with string
• cal (18/49) Aug 20 2012 I have had to work around this also. One way is to first multiply
• Philippe Sigaud (12/24) Aug 23 2012 A possibility is to use a function template, passing the double as a
• timothee cour (3/18) Jan 01 2016 https://issues.dlang.org/show_bug.cgi?id=15497

Bobby Bingham <uhmmmm gmail.com> writes:

I'm just getting started with D, and was playing around with string
mixins.  I've hit a snag, and have reduced it to a minimal test case:

    import std.conv;

    string test()
    {
        return to!string(0.0);
    }

    immutable auto testvar = mixin(test());

This gives this result when compiling:

/usr/include/phobos2/std/format.d(1479): Error: snprintf cannot be interpreted
at compile time, because it has no available source code
/usr/include/phobos2/std/conv.d(99):        called from here:
formatValue(w,src,f)
/usr/include/phobos2/std/conv.d(824):        called from here: toStr(value)
/usr/include/phobos2/std/conv.d(268):        called from here: toImpl(_param_0)
test.d(6):        called from here: to(0)
test.d(9):        called from here: test()
test.d(9): Error: argument to mixin must be a string, not (test())

I guess converting a double to a string can't be done at compile time
because it requires calling the C snprintf function?  It compiles fine
if I replace the 0.0 with an int literal.  Is there any way around
this limitation?

"cal" <callumenator gmail.com> writes:

On Tuesday, 21 August 2012 at 04:43:09 UTC, Bobby Bingham wrote:
 I'm just getting started with D, and was playing around with 
 string
 mixins.  I've hit a snag, and have reduced it to a minimal test 
 case:

     import std.conv;

     string test()
     {
         return to!string(0.0);
     }

     immutable auto testvar = mixin(test());

 This gives this result when compiling:

 /usr/include/phobos2/std/format.d(1479): Error: snprintf cannot 
 be interpreted at compile time, because it has no available 
 source code
 /usr/include/phobos2/std/conv.d(99):        called from here: 
 formatValue(w,src,f)
 /usr/include/phobos2/std/conv.d(824):        called from here: 
 toStr(value)
 /usr/include/phobos2/std/conv.d(268):        called from here: 
 toImpl(_param_0)
 test.d(6):        called from here: to(0)
 test.d(9):        called from here: test()
 test.d(9): Error: argument to mixin must be a string, not 
 (test())

 I guess converting a double to a string can't be done at 
 compile time
 because it requires calling the C snprintf function?  It 
 compiles fine
 if I replace the 0.0 with an int literal.  Is there any way 
 around
 this limitation?

I have had to work around this also. One way is to first multiply 
your float by a large factor (say 10000 depending on what 
precision you want) and then adding a decimal point back in to 
the string. Kinda hacky, but... Here is an example:

int fx = cast(int) (cos(angle)*1000000.);
string fsx = fx.to!string;

string xprefix;
if (fsx[0] == '-')
{
   xprefix = "-";
   fsx = fsx[1..$];
}

if (fsx.length == 7)
   sx = xprefix ~ fsx[0] ~ "." ~ fsx[1..$];
else
   sx = xprefix ~ "0." ~ fsx;

sx is then the string you want to mixin.

Philippe Sigaud <philippe.sigaud gmail.com> writes:

On Tue, Aug 21, 2012 at 6:43 AM, Bobby Bingham <uhmmmm gmail.com> wrote:
 I'm just getting started with D, and was playing around with string
 mixins.  I've hit a snag, and have reduced it to a minimal test case:

     import std.conv;

     string test()
     {
         return to!string(0.0);
     }

     immutable auto testvar = mixin(test());

 I guess converting a double to a string can't be done at compile time
 because it requires calling the C snprintf function?  It compiles fine
 if I replace the 0.0 with an int literal.  Is there any way around
 this limitation?

A possibility is to use a function template, passing the double as a
template argument:

string test(double d)() // d is a template argument
{
    return d.stringof;
}

enum testvar = mixin(test!(3.14));

void main()
{
    pragma(msg, testvar);
}

timothee cour <thelastmammoth gmail.com> writes:

On Thursday, 23 August 2012 at 13:56:05 UTC, Philippe Sigaud 
wrote:
 On Tue, Aug 21, 2012 at 6:43 AM, Bobby Bingham 
 <uhmmmm gmail.com> wrote:
[...]

 [...]

 A possibility is to use a function template, passing the double 
 as a template argument:

 string test(double d)() // d is a template argument
 {
     return d.stringof;
 }

 enum testvar = mixin(test!(3.14));

 void main()
 {
     pragma(msg, testvar);
 }

https://issues.dlang.org/show_bug.cgi?id=15497