<?php
namespace Encase\Functional;
/**
* Extract a portion of an array, string or \Traversable object.
* Sliced traversables are returned as arrays.
*
* Will try to use native PHP functions where possible.
*
* @see https://php.net/manual/en/function.array-slice.php
* @see https://php.net/manual/en/function.mb-substr.php
* @see https://php.net/manual/en/function.iterator-to-array.php
*
* @param array|string $value
* @param int|null $start Where to begin extraction.
* @param int|null $size Where to end extraction.
* @return mixed A slice of $value.
*/
function slice($value, ?int $start, int $end = null)
{
$type = assertType($value, ['\Traversable', 'iterable', 'string'], 'value');
$start = $start ?? 0;
// Figure out the slice size as PHP funcs expect sizes rather than indexes.
if ($end !== null) {
if ($start && ($end > 0 || $start < 0) && $end < $start) {
[$start, $end] = [$end, $start];
}
$size = $end < 0 ? $end : $end - $start;
} else {
$size = null;
}
// Implement strings using unicode-aware (where possible) substr.
// TODO: make mb_* a requirement of the library?
if ($type === 'string') {
return \function_exists('mb_substr') ?
\mb_substr($value, $start, $size) :
\substr($value, $start, $size);
}
// If the value is traversable, we can extract with a foreach loop.
if ($type === '\Traversable') {
// Try to use PHP's iterator_to_array for classes implementing
// \IteratorAggreggate.
if ($value instanceof \IteratorAggregate && $start > 0) {
if ($size <= 0) {
$size = -1;
}
$value = \iterator_to_array(
new \LimitIterator($value->getIterator(), $start, $size), true
);
$start = 0;
} else {
// Fall back to a foreach by building an array out of the iterator. If
// we have a positive $size we can stop early and return that array.
// If not, we'll fall back with array_slice with a $start of 0.
$output = [];
foreach ($value as $key => $value) {
if ($start > 0) {
--$start;
continue;
}
$output[$key] = $value;
if ($size !== null && $size > 0) {
--$size;
if (!$size) {
return $output;
}
}
}
$value = $output;
}
}
return \array_slice($value, $start, $size, true);
}
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