Utf8 to Utf32 cast cost

[Daniel Kozak via Digitalmars-d-learn]

On Monday, 8 June 2015 at 11:06:07 UTC, Daniel Kozák wrote:
>
> On Mon, 08 Jun 2015 10:51:53 +0000
> weaselcat via Digitalmars-d-learn 
> <digitalmars-d-learn at puremagic.com>
> wrote:
>
>> On Monday, 8 June 2015 at 10:49:59 UTC, Ilya Yaroshenko wrote:
>> > On Monday, 8 June 2015 at 10:42:00 UTC, Kadir Erdem Demir 
>> > wrote:
>> >> I want to use my char array with awesome, cool 
>> >> std.algorithm functions. Since many of this algorithms 
>> >> requires like slicing etc.. I prefer to create my string 
>> >> with Utf32 chars. But by default all strings literals are 
>> >> Utf8 for performance.
>> >>
>> >> With my current knowledge I use to!dhar to convert 
>> >> Utf8[](or char[]) to Utf32[](or dchar[])
>> >>
>> >> dchar[] range = to!dchar("erdem".dup)
>> >>
>> >> How costly is this?
>> >> Is there a way which I can have Utf32 string directly 
>> >> without a cast?
>> >
>> > 1. dstring range = to!dstring("erdem"); //without dup
>> > 2. dchar[] range = to!(dchar[])("erdem"); //mutable
>> > 3. dstring range = "erdem"d; //directly
>> > 4. dchar[] range = "erdem"d.dup; //mutable
>> 
>> what's wrong with http://dlang.org/phobos/std_utf.html#.toUTF32
>
> from: http://dlang.org/phobos/std_encoding.html#.transcode
>
> Supersedes:
> This function supersedes std.utf.toUTF8(), std.utf.toUTF16() and
> std.utf.toUTF32() (but note that to!() supersedes it more 
> conveniently).

BTW on ldc(ldc -O3 -singleobj -release -boundscheck=off) 
transcode is the fastest:

f0 time: 1 sec, 115 ms, 48 μs, and 7 hnsecs // to!dstring
f1 time: 449 ms and 329 μs // toUTF32
f2 time: 272 ms, 969 μs, and 1 hnsec // transcode