NAME

Set::Window - Manages an interval on the integer line

SYNOPSIS

  use Set::Window;
  
  $window  = new_lr Set::Window $left, $right;
  $window  = new_ll Set::Window $left, $length;
  $window  = empty  Set::Window;
  
  $left     = $window->left;
  $right    = $window->right;
  $size     = $window->size;  
  @bounds   = $window->bounds;
  @elements = $window->elements;
  
  empty     $window;
  eqivalent $window1 $window2;
  equal     $window1 $window2;
  
  $window = copy        $window
  $window = offset      $window $offset
  $window = inset       $window $inset
  $window = cover       $window @windows
  $window = intersect   $window @windows
  
  @windows = $window->series($length);

REQUIRES

Perl 5.6.0, Exporter

EXPORTS

Nothing

DESCRIPTION

A Set::Window object represents a window on the integer line; that is, a finite set of consecutive integers.

Methods are provided for creating and modifying windows, for obtaining information about windows, and for performing some simple set operations on windows.

The empty window

The empty window represents the empty set. Like the empty set, the empty window is unique.

METHODS

Creation

new_lr Set::Window $left, $right

Creates and returns a new Set::Window object. $left and $right specify the first and last integers in the window.

If $right is less than $left, returns the empty window.

new_ll Set::Window $left, $length

Creates and returns a new Set::Window object. $left is the first integer in the interval, and $length is the number of integers in the interval

If $length is less than one, returns the empty window.

empty Set::Window

Creates and returns an empty Set::Window object.

Access

$window->left

Returns the first integer in the window, or undef if $window is empty.

$window->right

Returns the last integer in the window, or undef if $window is empty.

$window->size

Returns the number of integers in the window.

The identity $window->size == $window->right - $window->left + 1 holds for all non-empty windows.

$window->bounds

Returns a list of the first and last integers in $window, or undef if $window is empty. In scalar context, returns an array reference.

$window->elements

Returns a list of the integers in $window, in order. In scalar context, returns an array reference.

Predicates

empty $window

Returns true iff $window is empty.

equal $window1 $window2

Returns true iff $window1 and $window2 are the same.

All empty windows are equal.

equivalent $window1 $window2

Returns true iff $window1 and $window2 are the same size.

Modification

These methods implement copy semantics: modifications are made to a copy of the original window. The original window is unaltered, and the new window is returned.

copy $window

Creates and returns a (deep) copy of $window.

offset $window $offset

Makes a copy of $window, and then shifts it by $offset. Positive values of $offset move the window to the right; negative values move it to the left. Returns the new window.

If offset is called on the empty window, it returns the empty window.

inset $window $inset

Makes a copy of $window, and then shrinks it by $inset at each end. If $inset is negative, the window expands. Returns the new window.

If inset is called on the empty window, it returns the empty window.

cover $window @windows

Creates and returns the smallest window that covers (i.e. contains) $window and all the @windows.

intersect $window @windows

Creates and returns the largest window that is contained by $window and all the @windows. This may be the empty window.

Utility

$window->series($length)

Returns a list of all the windows of $length that are contained in $window, ordered from left to right. In scalar context, returns an array reference.

If $length is greater than $window->length, the list will be empty. If $length is less than 1, returns undef.

DIAGNOSTICS

None.

NOTES

Why?

Belive it or not, I actually needed this structure in a program. Maybe someone else will need it, too.

Weight

Set::Window objects are designed to be lightweight. If you need more functionality, consider using Set::IntSpan.

Error handling

Set::Window does not issue any diganostics; in particular, none of the methods can die.

Calling elements on a large window can lead to an out of memory! message, which cannot be trapped (as of perl 5.003). Applications that must retain control can protect calls to elements with an intersect

  $limit = new_lr Set::Window -1_000_000, 1_000_000;
  @elements = $window->intersect($limit)->elements;

or check the size of $window first:

  length $window < 2_000_000 and @elements = elements $window;

Operations involving the empty window are handled consistently. They return valid results if they make sense, and undef otherwise. Thus:

  Set::Window->empty->elements

returns an empty list, because the empty window has no elements, while

  Set::Windows->empty->bounds

returns undef, because the empty window has no first or last element.

SEE ALSO

perl(1), Set::IntSpan

AUTHOR

Steven McDougall, swmcd@world.std.com

COPYRIGHT

Copyright 1996-200 by Steven McDougall. All rights reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

cpanm Set::Window

perl -MCPAN -e shell
install Set::Window