Re^2: Spotting an empty array as argument

Right, I suspected there might not be any nice way of doing it. I mean, "say" does seem to do some magic in the "no argument" case, just like "print", since it treats it differently from the "empty array" case. But maybe that's just a special rule for built-in functions.

It's weird though, because there are so many built-in functions that have the same behaviour, defaulting to $_ if there are no arguments, and it's clearly useful, so it's surprising if there's no way of recreating that for your own functions.

Comment on Re^2: Spotting an empty array as argument

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Re^3: Spotting an empty array as argument by choroba (Cardinal) on Mar 25, 2021 at 21:39 UTC
The prototype `(_)` can be used for the last argument. Some builtin functions can't be simulated, though, you can detect them by `prototype('CORE::func')` returning undef. For example, you can easily replicate the behaviour of uc, as `prototype('CORE::uc')` returns `_`. Similarly, pack has the prototype of `$_` (the underscore must be the last one). But print or chomp return undef, so their behaviour is more complex and prototypes can't express it. So there is a special rule, but only for some of the built-in functions. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re^4: Spotting an empty array as argument by ikegami (Patriarch) on Mar 26, 2021 at 19:32 UTC
While `prototype` would normally be a useful thing to try, `say` can't be prototyped because it supports `say FH ...`, so a definitive answer can't be obtained from `prototype` here (assuming the lack of file handle support is acceptable). Seeking work! You can reach me at ikegami@adaelis.com	[reply] [d/l] [select]
Re^5: Spotting an empty array as argument by LanX (Saint) on Mar 26, 2021 at 20:36 UTC
> say can't be prototyped because it supports say FH ..., I can't follow, the fact that `say` is internally calling something like `FH->print(@_,"\n")` shouldn't have any consequence on the prototype. Hmmm ... I think what you mean is that this inhibits attempts to override `say` with another implementation, since it needs to act like an indirect method call, but with prototype magic. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^6: Spotting an empty array as argument by ikegami (Patriarch) on Mar 27, 2021 at 05:56 UTC
Re^4: Spotting an empty array as argument (prototype _ ) by LanX (Saint) on Mar 26, 2021 at 10:46 UTC
> (the underscore must be the last one) FWIW, the last of the mandatory ones! I.e. you can define following prototypes as long as they are marked optional with a semicolon. Trouble here is the scalar context! `DB<237> sub tst (_;@) { dd \@_ } DB<238> $_=666; @a='a'..'c'; $a='A' DB<239> tst [666] DB<240> tst $a,1,2,3 ["A", 1, 2, 3] DB<241> tst $a,@a ["A", "a", "b", "c"] DB<242> tst @a # OOPS [3]` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]


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