Re: Questions about context


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Re: Questions about context

by Revelation (Deacon)

on Jan 30, 2005 at 20:15 UTC ( [id://426417]=note: print w/replies, xml )

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in reply to Questions about context

It's important to note that arrays and lists are not equivalent. With regards to (caller 0)[3] and (localtime)[5]+1900 the parentheses are forcing the evaluation of the list like an array. Lists, which are usually diagramed as (LIST) in Perl can be subscripted like a normal array. However, to do so the a slice syntax is used, which takes the form @result/$result = ( LIST ) [ LIST ];. The parens are used to avoid ambiguity. Merlyn could further clarify.

Thus,

my $scalar= ( EXPR )[0];
[download]

is the rough equivalent of:

my $scalar;
{
  my @expr = EXPR();
  $scalar = @expr[0]; # or $expr[0];
}
[download]

Gyan Kapur

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Re^2: Questions about context
by rir (Vicar) on Jan 31, 2005 at 22:34 UTC

(localtime)[5]+1900 the parentheses are forcing the evaluation of the list like an array.

It is a misleading statement. The parentheses are only for grouping. localtime[5] will convert [5] into an array of date and time elements. This is not what you want because [5] is not a reasonable thing to convert to a time.

The parentheses are only to get localtime to be called without an argument.

Enclosing parentheses don't change context. Look up the dual-nature comma operator to understand lists and their parentheses. That the standard (i.e. Camel) example of a list includes parentheses doesn't aid proper understanding of this issue. But it is impressive how the dwimery works in spite of this.

Be well,
rir

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