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=head1 TITLE
Optional 2nd argument to pop() and shift()
=head1 VERSION
Maintainer: Jonathan Scott Duff <[EMAIL PROTECTED]>
Date: 7 Aug 2000
Version: 1
Mailing List: [EMAIL PROTECTED]
Number: 56
=head1 ABSTRACT
The inverse operations to C and C both accept a LIST to
"add" to an array, yet C and C only remove B element
from an array. In the interest of symmetry and TMTOWTDI, C and
C should allow the programmer to remove multiple items from an
array.
=head1 DESCRIPTION
The intent should be obvious, but I'll point it out anyway.
=head2 pop
The documentation for Perl 5.6.0 states that pop has one of two forms:
C, or just C. This RFC proposes that a third form be
added to C
=over 4
=item pop ARRAY, EXPR
EXPR would be evaluated to determine the number of elements to remove
from the end of ARRAY and that number would be removed and returned.
Thus C would be a more natural inverse to C (If you can
add multiple elements to an array with C, why can't you remove
multiple elements from an array with C?)
=back
This functionality can currently be accomplished with C, but
it is non-obvious that C should be the routine to call and
the method isn't at all intuitive. To "pop" the last $N items off of
the end of an array using C, the call looks like this:
splice @array, -$N; # remove the last $N items
contrast to the more natural looking
pop @array, $N; # remove the last $N items
=head2 shift
The semantics for C are similar to C except that it
operates on the other end of the array. C also suffers from
the inability to shift more than one element from the array. Just
like C, the two forms of C are a C, and
just plain C. This RFC proposes that a third form be added:
=over 4
=item shift ARRAY, EXPR
EXPR would be evaluated to determine the number of elements to remove
from the beginning of ARRAY and that number would be removed and returned.
Thus, C would be a more natural inverse to C. (If
you can add multiple elements to an array with C, why can't
you remove multiple elements with C?)
=back
As with C the proposed semantics can be accomplished with
C and are just as un-intuitive:
splice @array, 0, $N; # remove the first $N elements
contrast to
shift @array, $N; # remove the first $N elements
=head2 Random examples
@numbers = 1..10;
$ten = pop @numbers;# still works
@popped = pop @numbers, 3; # Take away 7, 8, 9
push @numbers, @popped; # Put 'em back
@popped = pop @numbers, 0; # Nothing happens
@popped = pop @numbers, 9; # And then there were none.
@numbers = 1..10;
@popped = pop @numbers, 100;# And then there were none but
# @popped only has 10 things
@numbers = 1..10;
$one = shift @numbers; # still works
@shifted = shift @numbers, 3; # Take away 2, 3, and 4
unshift @numbers, @shifted; # Put 'em back
@shifted = shift @numbers, 0; # Nothing happens
@shifted = shift @numbers, 9; # And then there were none.
@numbers = 1..10;
@shifted = shift @numbers, 100; # And then there were none but
# @shifted only has 10 things
=head1 IMPLEMENTATION
I don't know the gory details other than it should be possible.
However, there is one implementation detail that occurs to me:
What should happen when the expression given to C, or
C evaluates to a negative number? I see three options:
1) Nothing. We can only pop/shift positive amounts
2) Act as if the number were positive (i.e. abs(EXPR))
3) C would then act as C and C would
act as C
The author of this RFC sees arguments for all three.
=head1 REFERENCES
The Perl 5.6.0 documentation
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