Re: Fastest way to check if a predicate can take a single parameter of a specific type

[Paul Backus via Digitalmars-d-learn]

On Friday, 11 October 2019 at 09:05:25 UTC, Per Nordlöw wrote:
I want to check whether
    auto _ = pred(T.init);
    static assert(is(typeof(_) == bool));

compiles or not.

Which one

    __traits(compiles, { auto _ = pred(T.init); static 
assert(is(typeof(_) == bool)); })

and

    is(typeof(pred(T.init)) == bool)

is preferred compilation performance-wise?

Seems like the second one requires strictly less semantic 
analysis and is shorter and easier to read, so I'd go with that.

Note that `pred(T.init)` will fail if pred accepts its argument 
by ref. If you want to handle that case, you have to do something 
like

    is(ReturnType!((T arg) => pred(arg)) == bool))