Function Alpha.isValidAlpha
Reports whether alpha is a usable opacity from 0 through 1.
bool isValidAlpha() const pure nothrow @nogc @property @safe;
Returns false for values below 0, above 1, NaN, and infinities.
The check does not clamp or otherwise modify the value.
Example
const value = Alpha!SRgbf(SRgbf(0.2f, 0.4f, 0.8f), 0.5f);
assert(value .isValidAlpha);
}