whereas the other two use AUTOLOAD to create the subs in their own package space and then &goto them...every time they are used.
Eh, no. The first time they are used AUTOLOAD creates them and &gotos in them. The second time, the sub is there and the sub is called.

The difference is that Errno defines all the subs at compile time - they are empty prototyped subs returning a single value - and are hence are being constant folded at compile time. If you use EAGAIN, Perl will substitute the appropriate value at compile time - which avoids all the overhead of calling a subroutine at run time.

The benchmark is biased towards heavy use of constants. A typical program will only use a few constants, and only a few times in a program. That means that if you'd export a lot of constants the way Errno does, you pay a heavier price at compile time, regardless how often, and how many constants you use. Fcntl however avoids the costs of compiling all the subs you aren't going to use - but the price of using a constant goes up.

Perl --((8:>*

In reply to Re^2: Slow constants by Perl Mouse
in thread Slow constants by powerman

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