Utf8 to Utf32 cast cost

[Kadir Erdem Demir via Digitalmars-d-learn]

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?