Is using constants slower than using variables

Considering that Perl doesn't have constants, the question isn't clear. It will depend on what you consider a constant. Many people consider a variable in all caps to be a constant. That of course is as fast as using constants.

Others use "use constant" or tiny subs with an empty prototype returning a literal as constants. Are they faster than variables? Well, that depends. If it's just fetching a value (read access), yes, then they are faster as the fetch can be done at compile time. But such constants lack a sigil. So you cannot easily interpolate them. Hence, you might write:

    printf "The value is %d.\n", CONSTANT;
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instead of

    print "The value is $CONSTANT.\n";
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The former means parsing a format, and substituting. That may very well be slower than the interpolation.

Now, you are using methods as constants. I haven't benchmarked it, but I'd be quite surprised if that wasn't the slowest solution of the three (variable, empty prototype sub, method).

Personally, I prefer variable. In all caps. Speed difference isn't an issue for me. Variables interpolate; subs and methods don't. If I want to trap a possible assignment to such a variable, I use Readonly. But usually, I do not care. If someone wants to assign to something that's supposed to constant, it's their own responsibility. Who am I to stop them?