Re^2: Label makes a sub to return empty list -- "secret"? documented?

Thanks, everyone. FWIW (I usually distrust multi-millions-per-sec benchmarks):

cmpthese 5e7, {
    1 => sub { my $x = 1 + 1; return },
    2 => sub { my $x = 1 + 1; () },
    3 => sub { my $x = 1 + 1; _: },
};

1 27367269/s   -- -13% -22%
2 31367629/s  15%   -- -11%
3 35161744/s  28%  12%   --
[download]

"Perl subs are expensive"? The cheapest adjustment is just above. Otoh, now I have a justification (not that I need any or anyone cares) not to follow PBP's "Place the label on the line preceding the loop keyword" -- just in case, easier and safer while debugging and commenting-out this or that, to keep label and code on the same line.

Comment on Re^2: Label makes a sub to return empty list -- "secret"? documented? Download Code

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Re^3: Label makes a sub to return empty list -- "secret"? documented? by ikegami (Patriarch) on Sep 13, 2025 at 04:09 UTC
Sometimes, I prefer to invert the numbers to get the time saved to put things into perspective. `27367269 calls/s = 37 ns/call 31367629 calls/s = 32 ns/call 35161744 calls/s = 28 ns/call` [download] So `_:` is 9 ns faster than `return` (assuming the numbers are meaningful). After 100 million calls, you still wouldn't have saved a second by switching from `return` to `_:`. Update: I had moved a decimal point in the wrong direction. Fixed.	[reply] [d/l] [select]
Re^4: Label makes a sub to return empty list -- "secret"? documented? by hippo (Archbishop) on Sep 13, 2025 at 09:26 UTC
27367269 calls/s = 0.365 ns/call I think your numbers are a couple of orders of magnitude out. By my maths 1 / 27367269 = 0.0000000365, so that's 36.5ns per call. Even so, your point is valid. It is only in extreme cases where any of this is really worth worrying about. 🦛	[reply]
Re^5: Label makes a sub to return empty list -- "secret"? documented? by ikegami (Patriarch) on Sep 13, 2025 at 14:48 UTC
The numbers seemed absurd, but I was too tired to register I needed to redo the math. I had moved a decimal point in the wrong direction. Fixed.	[reply]
Re^3: Label makes a sub to return empty list -- "secret"? documented? by LanX (Saint) on Sep 13, 2025 at 23:23 UTC
> Otoh, now I have a justification (not that I need any or anyone cares) not to follow PBP's "Place the label on the line preceding the loop keyword" -- That's a weird logical construct There was no indication or benchmark in this thread so far that placing a label at a previous line comes with a notable performance overhead. Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery}	[reply]
Re^4: Label makes a sub to return empty list -- "secret"? documented? by Anonymous Monk on Sep 14, 2025 at 18:44 UTC
It's not performance this time. Intuitively, labels belong to the same "subordinate" "category" as e.g. semicolons, both not far from comments and white-space. Extra semicolon at the end of a block doesn't change what this block evaluates to. Lone label, I now know, does, which is dangerous. Neglected to have been (temporarily?) commented-out along with its loop (if placed per PBP at the next line) and maybe some further statements. Of course, it's the same weird nonsense, please ignore.	[reply]
Re^5: Label makes a sub to return empty list -- "secret"? documented? by LanX (Saint) on Sep 14, 2025 at 20:48 UTC
OK I see your point now, but it's a bit contrived to have expectations about the new return value after commenting a trailing loop out. (IIRC is the return value of a loop not defined.) Anyway thanks for the discussion, I learned something new. :) Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery}	[reply]