Re^3: Performance Trap - Opening/Closing Files Inside a Loop

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Re^4: Performance Trap - Opening/Closing Files Inside a Loop by Animator (Hermit) on Dec 10, 2004 at 12:38 UTC
It shouldn't (or atleast not as far as I know)	[reply]
Re^4: Performance Trap - Opening/Closing Files Inside a Loop by Ven'Tatsu (Deacon) on Dec 10, 2004 at 16:47 UTC
Variable declaration with a statment modifier can have stange effects, usally a lexical not getting cleared as expected, due to `my` having both runtime and compile time effects, the test only blocks the runtime effect of resetting the variable. This can be used for some interesting obfu but should be avoided in serious code IMO. `# if EXPR is false $foo will still have the last set value for this sc +ope's (but not other scope's) $foo my $foo if EXPR; #same here if EXPR is false the first time it's tested on this pass. my $bar while EXPR;` [download] It's rather common to stick a declaration inside the test of a (BLOCK) loop, often seen with input loops, or looping over both keys and values of a hash at the same time. `while (my $foo = <$fh>) { #do something } while (my ($key, $value) = each %hash) { #do other things }` [download]	[reply] [d/l] [select]
Re^4: Performance Trap - Opening/Closing Files Inside a Loop by diotalevi (Canon) on Dec 10, 2004 at 16:42 UTC
You're thinking of my() on statements using modifiers. The problem is avoiding only calling my() sometimes. Then the variable may retain is previous value from earlier loops in a way that is declared off-limits and buggy but never fixed because it would be too much overhead to make it consistent. Ok `while ( my ( $k, $v ) = each %h ) { ... } while ( my $line = <> ) { ... } for ( my $ix = 0; ...; ... ) { ... }` [download] Not ok `my $... = ... if ...; ... or my $... = ...;` [download]	[reply] [d/l] [select]