I do agree that custom identifiers are slower, hence my alias calculate { example for $calculate() being a clone of $calc().

But, if we combine these sources for the built-in identifier, $isodd().

Code:
alias isodd {
if ($calc(X % 2)) {
  ; X is odd
}
if (X & 1) {
  ; X is odd
}
if ($right(X,1) isin 13579) {
  ; X is odd.
}
if ($and(X,1)) {
  ; X is odd.
}
if (. isin $calc(X / 2)) {
  ; X is odd
}
}


Then, I would have to say, the built-in identifier is slower.

The problem is I pasted the above in mIRC scripting, when in fact, Khaled codes identifiers in C++ or something.

Therefore, if you used only 1 of the above code, for your custom--identifier, then it would be faster.

But before that, it just simply depends on the code source. It's possible that a build-in identifier could be so complex (from checking all the possibilities) that simply using a custom identifier is faster.

And I guess a built-in $isodd identifier, would not be as combined. You could code a non-built $isodd extremely complex, whereas a very simple custom-identifier could be faster. But of course, none of us could know that unless we see Khaled's built source.