scope of my $x in if statements

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Re: scope of my $x in if statements by ikegami (Patriarch) on May 07, 2009 at 20:50 UTC
I want the $x in g($x) to reference the lexical $x on the same line. That's currently not possible in order to allow `my $x = $x; # Initialize with value from outer scope.` [download] The clearest alternative is probably `my $x = f(); if ($x and g($x)) { ... }` [download] or `if (my $x = f()) { if (g($x)) { ... } }` [download]	[reply] [d/l] [select]
Re^2: scope of my $x in if statements by ig (Vicar) on May 08, 2009 at 01:32 UTC
The first expands the scope of $x.	[reply]
Re^3: scope of my $x in if statements by ikegami (Patriarch) on May 08, 2009 at 01:54 UTC
So?	[reply]
Re^4: scope of my $x in if statements by ig (Vicar) on May 08, 2009 at 02:05 UTC
Re^5: scope of my $x in if statements by ikegami (Patriarch) on May 08, 2009 at 03:32 UTC
Some notes below your chosen depth have not been shown here
Re: scope of my $x in if statements by FunkyMonk (Bishop) on May 07, 2009 at 21:00 UTC
There's the utterly hideous use of do: `if (do {my $x = f(); $x and g($x)}) { ... }` [download] but, please, just use ikegami's suggestion	[reply] [d/l]
Re^2: scope of my $x in if statements by ikegami (Patriarch) on May 07, 2009 at 21:07 UTC
Speaking of hideous, the functional approach written in Perl: `if (my $x = x(f(), \&g)) { ... }` [download] having defined x() as `sub x { my ($x, $g) = @_; $x && $g->($x) }` [download]	[reply] [d/l] [select]
Re^2: scope of my $x in if statements by shmem (Chancellor) on May 07, 2009 at 21:48 UTC
not either, because the scope of `$x` is confined to the do block: `use strict; use warnings; sub f{0} sub g{1} if (do {my $x = f(); $x and g($x)}) { print "cheerful: $x\n"; } __END__ Global symbol "$x" requires explicit package name at scope.pl line 6.` [download]	[reply] [d/l] [select]
Re^3: scope of my $x in if statements by ikegami (Patriarch) on May 07, 2009 at 22:23 UTC
`if (my $x = do {my $x = f(); $x and g($x)}) { print "cheerful: $x\n"; }` [download]	[reply] [d/l]
Re^4: scope of my $x in if statements by shmem (Chancellor) on May 07, 2009 at 22:35 UTC
Re: scope of my $x in if statements by moritz (Cardinal) on May 07, 2009 at 20:36 UTC
I don't think this works in Perl 5, the variable is only visible in the statement after the declaration. It works in Perl 6, though: `$ perl6 -e 'sub f { 3 }; sub g($a) { $a }; if my $x = f() and g($x) { +say "works" }' works` [download]	[reply] [d/l]
Re: scope of my $x in if statements by mikeraz (Friar) on May 07, 2009 at 20:35 UTC
Setting aside why you want to do this, how about: `#!/usr/bin/env perl use strict; sub f { return 2; } sub g { my ($y) = shift @_; return $y2; } if ( my $k = g(my $x = f()) ) { print "If the answer is four I'm happy. Answer == $k\n"; }` [download] That example seems to do all that you want. update*: Test platform was perl v5.8.6 Be Appropriate && Follow Your Curiosity	[reply] [d/l]
Re^2: scope of my $x in if statements by ikegami (Patriarch) on May 07, 2009 at 20:49 UTC
That's not equivalent. It can have a different result when f() returns something false	[reply]
Re^3: scope of my $x in if statements by mikeraz (Friar) on May 07, 2009 at 20:54 UTC
Meaning if f() returns false and g(falsehood) returns true. Time to go work on my test case skills. Be Appropriate && Follow Your Curiosity	[reply]
Re^4: scope of my $x in if statements by ikegami (Patriarch) on May 07, 2009 at 21:05 UTC
Re: scope of my $x in if statements by NetWallah (Canon) on May 07, 2009 at 21:50 UTC
How about this readable alternative ? : `if( my $x = $_ = f() and g($_) ) {....}` [download] and if you REALLY need to modify $x inside g(): `if($_ = \(my $x = f()) and $$_ and g($$_) )` [download] Update: While I agree with ikegami's assessment below that this is not good practice, I maintain that this IS a solution to the problem posted by the O.P. ..to maintain is to slowly feel your soul, sanity and sentience ebb away as you become one with the Evil.	[reply] [d/l] [select]
Re^2: scope of my $x in if statements by ikegami (Patriarch) on May 07, 2009 at 22:21 UTC
Clobbering your caller's `$_` is bad (even in everyday scenarios), so you need to add `local`. When you do, you end up with the same problem and nothing is solved.	[reply] [d/l] [select]
Re: scope of my $x in if statements by ig (Vicar) on May 08, 2009 at 01:38 UTC
I would probably do this as (or as nested if's as ikegami suggested): `{ my $x; if( $x = f() and g($x) ) { ... } }` [download] If you really didn't like the extra block/indent, you could also do: `{ last unless( my $x = f() ); last unless( g($x) ); ... }` [download]	[reply] [d/l] [select]