Re^2: Temp variable performance vs Inline behavior

BrowserUk’s solution:

my @devices = grep{ defined( $_ = parse_node( $_ ) ) } @nodes;
[download]

is compact and efficient, but has one side-effect: the assignment to $_ clobbers the contents of @nodes.

In cases where this is undesirable, the following seems to do the same without the side-effect:

my @devices = grep { defined } map { parse_node( $_ ) } @nodes;
[download]

Or is there a simpler way?

Athanasius <°(((>< contra mundum

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Re^3: Temp variable performace vs Inline behavior by tobyink (Canon) on Jun 27, 2012 at 16:44 UTC
You could use the same technique but clobber a temporary array instead... `my @devices = grep { defined($_ = parse_node($_)) } my @tmp = @nodes;` [download] Or you could use map: `my @devices = map { my $x; defined($x=parse_node($_)) ? $x : () } @nodes;` [download] If `parse_node` was written to return the empty list in cases of failure (rather than returning the scalar undef), then it would just be: `my @devices = map { parse_node($_) } @nodes;` [download] `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]

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You could use the same technique but clobber a temporary array instead...

my @devices =
  grep { defined($_ = parse_node($_)) }
  my @tmp = @nodes;
[download]

Or you could use map:

my @devices =
  map { my $x; defined($x=parse_node($_)) ? $x : () }
  @nodes;
[download]

If parse_node was written to return the empty list in cases of failure (rather than returning the scalar undef), then it would just be:

my @devices = map { parse_node($_) } @nodes;
[download]

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'