What's equivalent to C#'s select?

[Marc]

On Monday, 15 January 2018 at 07:37:42 UTC, Simen Kjærås wrote:
> On Sunday, 14 January 2018 at 22:07:22 UTC, Marc wrote:
>> thanks, can i use it at compile time as well?
>>
>>>	enum isMutableString(string field) = 
>>>is(typeof(__traits(getMember, >C, field)) == string);
>>>	static foreach(field; [FieldNameTuple!C].filter!(f =>
>>>>isMutableString!(f))) {
>>>		writeln(field);
>>>	}
>
> You're mixing compile-time and run-time logic here in a way 
> that D doesn't allow. In particular, isMutableString requires 
> the passed string to be a compile-time constant, and filter 
> works on run-time values.

I just thought that filter() could be evaluated at compile time 
too, as others function that I've used so far. Sometimes I don't 
know if a native function can be evaluated at compile time until 
I do enum x = func();

> There are a few different ways to resolve this. First, std.meta 
> has the Filter template, which behaves much in the same way as 
> std.algorithm.filter, but with compile-time tuples:
>
> static foreach (field; Filter!(isMutableString, 
> FieldNameTuple!C)) {
>     writeln(field);
> }
>
> The other option is to rewrite isMutableString to work with 
> run-time values:
>
> bool isMutableString(string field) {
>     switch (field) {
>         foreach (cField; FieldNameTuple!C) {
>             case cField:
>                 return is(typeof(__traits(getMember, C, 
> cField)) == string);
>         }
>         default:
>             return false;
>     }
> }
> static foreach(field; [FieldNameTuple!C].filter!(f => 
> isMutableString(f))) {
>     writeln(field);
> }
>
> Both of these give the same output, and should be what you want.
>
> --
>   Simen

That's exactly it! That Filter() from std.algorithm works like I 
wanted :) nice solution also with rewrite the function to work 
with run-time so that i can use with filter() but if I want to 
have minimum runtime code to filter out immutable strings, the 
first one is better right?