Utf8 to Utf32 cast cost

[Ilya Yaroshenko via Digitalmars-d-learn]

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