std.algorithm.startsWith only predicate

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On Sunday, 18 October 2015 at 17:48:20 UTC, Freddy wrote:
> How do you call startsWith with only a predicate
> ---
> import std.algorithm;
> import std.ascii;
>
> bool iden(string str)
> {
>     return str.startsWith!(a => a.isAlpha || a == '_');
> }
> ---

Is this a simplified use case of some actual code you have? 
Otherwise, you can just do:


bool iden(string str)
{
     auto f = str.front;
     return f.isAlpha || f == '_';
}