pure format

[Ali Çehreli via Digitalmars-d]

On 06/04/2015 10:02 AM, Oleg B wrote:

 > I think toString for float must be pure, but in practice it's not.
 >
 > import std.stdio;
 > import std.string;
 > string test( float abc ) pure { return format( "abc: % 6.3f", abc ); }
 > void main() { writeln( test( 13.3 ) ); }
 >
 > $ rdmd purefmtfloating.d
 > purefmtfloating.d(3): Error: pure function 'purefmtfloating.test' cannot
 > call impure function 'std.format.format!(char, float).format'
 > Failed: ["dmd", "-v", "-o-", "purefmtfloating.d", "-I."]
 >
 > DMD64 v2.067.1
 >
 > It's a bug? I read what std.format.format using libc sprintf
 > 
http://www.digitalmars.com/d/archives/digitalmars/D/learn/std.conv.to_purity_68957.html 

 > and if it try it's not a bug...

Floating point operations share global state ("flags" or "attributes") 
for rounding mode, exception and trap handling. Perhaps that's why 
floating point format cannot be pure.

Ali