set context for method's return values

demoralizer has asked for the wisdom of the Perl Monks concerning the following question:

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Re: set context for method's return values by AlexP (Pilgrim) on Jan 25, 2022 at 06:51 UTC
I think you just need to correctly place the brackets: `print((split(",", "A,B,C,D"))[2]);` [download]	[reply] [d/l]
Re: set context for method's return values by Discipulus (Canon) on Jan 25, 2022 at 08:26 UTC
Hello demoralizer, you can also: `print +(split /,/, 'A,B,C,D')[2]` where the `+` sign avoid the warning `print (...) interpreted as function` > return value as an array .. Technically using `()` we are creating a list, not an array: we can access the Nth element but, for example, we cannot `push` to it. L* PS the phrase about parens was related to this usage, not their general use; see below.. There are no rules, there are no thumbs.. Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.	[reply] [d/l] [select]
Re^2: set context for method's return values by LanX (Saint) on Jan 25, 2022 at 10:20 UTC
> Technically using () we are creating a list, Sorry that's not fully correct, `()[]` resp. `(EXPR)[SLICE]` is "creating a list" `(EXPR)` alone affects only precedence, no list context is propagated. for completeness: `()` is an empty list `(EXPR)=` is a list assignment Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^3: set context for method's return values by rsFalse (Chaplain) on Jan 29, 2022 at 11:59 UTC
`>> <...> ()[] resp. (EXPR)[SLICE] is "creating a list"` Once I wrote more on this with examples: Forcing list context. Brackets (with list within) as an unary right-associative operator	[reply] [d/l]
Re^2: set context for method's return values by demoralizer (Beadle) on Jan 25, 2022 at 15:25 UTC
Every once in a while I see that plus sign you used to suppress warnings, but so far I haven't been able to find an explanation for it. Do you have any keywords for me to search for to dig a little deeper into this topic, please?	[reply]
Re^3: set context for method's return values by Fletch (Bishop) on Jan 25, 2022 at 15:40 UTC
Not exactly sure but "unary plus" might get you on the right track. Basically the plus doesn't change the value but tells the parser after it's seen `print` that the next parens it sees aren't for it ("I am altering the parse tree. Pray I don't alter it further." — Darth Syntaxus). The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l]
Re^3: set context for method's return values by ikegami (Patriarch) on Jan 25, 2022 at 17:23 UTC
My explanation of unary-"+"	[reply]
Re^3: set context for method's return values by BillKSmith (Monsignor) on Jan 26, 2022 at 14:16 UTC
The explanation of `+(` is in the first section of the documentation of print. Be careful not to follow the print keyword with a left parenthesis unless you want the corresponding right parenthesis to terminate the arguments to the print; put parentheses around all arguments (or interpose a +, but that doesn't look as good). Bill	[reply] [d/l]
Re^3: set context for method's return values (unary plus) by LanX (Saint) on Jan 25, 2022 at 16:36 UTC
I have to admit that it confused me for a long time too. I thought it's akin to `0+` which enforces scalar context and numeric casting (also in other languages like JS). But it's basically a No-OP which separates a function from the parens, such that the parens are not interpreted as part of the function call. It has sufficiently low precedence and doesn't meddle with context: `DB<9> say ("a".."c")[1] syntax error at (eval 18)[c:/Strawberry/perl/lib/perl5db.pl:738] line +2, near ")[" DB<10> say (("a".."c")[1]) # how it works b DB<11> say +("a".."c")[1] # avoid extra parens b DB<12> say +("a".."c")[1..2] # LIST uneffected bc DB<13>` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^4: set context for method's return values (unary plus) by rsFalse (Chaplain) on Jan 29, 2022 at 11:47 UTC
Re^4: set context for method's return values (unary plus) by demoralizer (Beadle) on Feb 01, 2022 at 07:47 UTC
Re: set context for method's return values by haukex (Archbishop) on Jan 25, 2022 at 06:51 UTC
You were close: `print( (split(",", "A,B,C,D"))[2] )` Nitpick: split is not a method, methods are called with `->`.	[reply] [d/l] [select]
Re^2: set context for method's return values by demoralizer (Beadle) on Jan 25, 2022 at 15:22 UTC
So close yet so far ;) Thanks to ALL of you for your helpful answers!	[reply]
Re: set context for method's return values by Marshall (Canon) on Jan 27, 2022 at 04:09 UTC
Your code: `print(split(",", "A,B,C,D")[2]);` [download] Yields: `syntax error at XXX.pl line YYY, near ")["` [download] I think what you want is: `print "",(split(",", "A,B,C,D"))[2];` [download] print can take a file handle as an optional arg and this can be confusing. putting a dummy null string in front disambiguates this. The split creates a list, put the list into paren and use the bracketed 2 to get C. Basically don't put a Perl variable or a function call immediately after the keyword "print". Adding more parens is a possible solution, but I prefer the above. Mileage varies.	[reply] [d/l] [select]
Re: set context for method's return values by rsFalse (Chaplain) on Jan 29, 2022 at 12:39 UTC
You are asking for elements of the list with `()[]` construction. Your list generating function may have its own parentheses depending of your preferred coding style: `f( list_of_operands )` vs. `f list_of_operands`. Later I call more perlish. In both cases if you need to apply one more function, you need either one more pair of parentheses (using former function writing style), either no-op `'+'` symbol before an opening paren which helps parser. Discipulus showed a code written with second style, saving two pairs of parentheses (Re: set context for method's return values). Also be aware of one more known perl bug: why does 'print ("hey)")' give a warning?	[reply] [d/l] [select]


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