Re: Easy Reference for Contexts

m/.../ returns true or false in scalar context m/.../g give you a list of matches in list context m/(...)/ can populate an array with whatever gets captured... (??) while( ) i.e. inside parenthesis is evaluated in scalar context? foreach( ) i.e. inside parenthesis is evaluated in list context? <STDIN> returns the next line of input in list context
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Well ... most of this can be tested interactively.

The inside context with wantarray the outside context behavior with print, print scalar and a void call.

For instance I doubted that scalar m// returns true or false (those identifiers don't exist in Perl), I thought it's the number of matches returned.

But I was wrong: :)

  DB<23> $_="aaa"
 
  DB<24> print scalar m/a/
1
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Cheers Rolf

UPDATE: Forgot to mention, you can also check the prototype for most builtins:

 perl -e 'print prototype "CORE::push","\n"'
\@@
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which is more complex than just void, list and scalar... check out perlsub for details.

And some builtins (like map) have such a "rich" syntax that they can't be expressed with prototypes.

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Re^2: Easy Reference for Contexts by tchrist (Pilgrim) on Apr 14, 2011 at 19:27 UTC
For instance I doubted that `scalar m//` returns true or false (those identifiers don't exist in Perl), I thought it's the number of matches returned. But I was wrong: :) `DB<23> $_="aaa" DB<24> print scalar m/a/ 1` [download] Anything in Perl is true or false. Or rather, `ANYTHING` is true but `undef` is false. 😋 Like the relops, `m//`, `s///`, and `y///` can all return the magical false value, that secret special value that nobody talks about: `% perl -wle 'printf "got %d matches\n", scalar ANYTHING =~ /nothing/'` *`got 0 matches`* So I shan’t, either. 😜	[reply] [d/l] [select]
Re^3: Easy Reference for Contexts by LanX (Saint) on Apr 15, 2011 at 10:11 UTC
> Or rather, ANYTHING is true but undef is false. Many things in Perl are evaluated to false in boolean context, not only `undef`. Cheers Rolf	[reply] [d/l]
Re^4: Easy Reference for Contexts by JavaFan (Canon) on Apr 15, 2011 at 10:48 UTC
Tom is right. ANYTHING is true: `$ perl -E 'say +ANYTHING ? "true" : "false"' true` [download]	[reply] [d/l]
Re^5: Easy Reference for Contexts by LanX (Saint) on Apr 15, 2011 at 11:14 UTC


Think about Loose Coupling
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