Trying to add automatic radix detection in std.conv.parse

[klb via Digitalmars-d-learn]

hello, I'd like to test if it's possible to add an automatic 
radix detection in std.conv, parse.

I've added...
------------------------
     if (s.length >= 2)
     {
         if (s[0..2] == "0x" || s[0..2] == "0X")
         {
             uint radix = 16;
             Source nbr = s[2..$];
             return .parse!Target(nbr, radix);
         }
         else if (s[0..2] == "0b" || s[0..2] == "0B")
         {
             uint radix = 2;
             Source nbr = s[2..$];
             return .parse!Target(nbr, radix);
         }
     }
------------------------

...to the first parse version. The (maybe `naive`) idea is to 
redirect to the right parse version if the prefixes are found.

But it seems to break the purity of format() because I get , when 
compiling phobos, the following errors:

------------------------
std\utf.d(71): Error: pure function 'std.utf.UTFException.this' 
cannot call impure function 'std.str
ing.format!(char, uint).format'
std\utf.d(71): Error: safe function 'std.utf.UTFException.this' 
cannot call system function 'std.str
ing.format!(char, uint).format'
std\uuid.d(1536): Error: pure function 
'std.uuid.UUIDParsingException.this' cannot call impure funct
ion 'std.string.format!(char, string, string, uint).format'
------------------------

What's wrong ?