What is a short, fast way of testing whether x in [a, b]?

[Enjoys Math via Digitalmars-d-learn]

On Monday, 8 February 2016 at 02:47:24 UTC, Enjoys Math wrote:
> Right now I'm using a logical ||:
>
> if (!(2*PI - EPS!float <= t1-t0 || t1-t0 <= 2*PI + EPS!float)) {
>
> But I'll be doing this a lot, so was wondering if there's a D 
> native way of doing it.
>
> Thanks.

Currently I have:

@property T EPS(T)() {
	static if (is(T == double)) {
		return 0.000_000_001;	
	}
	static if (is(T == float)) {
		return 0.000_001;	
	}
	static if (is(T == int)) {
		return 1;
	}
}

alias EPS!float EPSF;
alias EPS!double EPSD;

bool epsEq(T)(T x, T y) {
	return x >= y - EPS!T && x <= y + EPS!T;
}