add a staticIndexOf overload taking a pred

[dlangBugzillaToGithub]

b2.temp reported this on 2018-12-11T09:58:48Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=19475

CC List

• simen.kjaras

Description

Overloads of std.meta.staticIndexOf allow only to find an exact needle but in some case it more useful to get the index of something based on a predicate, for example to get the index of a compile time value that partially matches (e.g member value of a struct used as UDA).

It even may be better to name them firstStaticIndexOf lastStaticIndexOf

[dlangBugzillaToGithub]

simen.kjaras commented on 2018-12-11T13:52:18Z

This can be trivially done as a combination of existing templates:

import std.meta;

enum predStaticIndexOf(alias Fn, T...) = staticIndexOf!(true, staticMap!(Fn, T));

template MoreThan2(T...) {
    enum MoreThan2 = T[0] > 2;
}

unittest {
    static assert(predStaticIndexOf!(MoreThan2, 1,2,3) == 2);
}