List Comprehension¶
A list comprehension is an expression-level syntax for building a new collection by describing it declaratively: a source, a transformation, and an optional filter, all in a single readable expression, as in Python’s [x * 2 for x in items if x > 0] or Haskell’s [x * 2 | x <- items, x > 0]. It is meant to read like the set-builder notation it is named after.
Because it is a single expression rather than a sequence of statements, a list comprehension can be nested, assigned, or passed as an argument directly, and many languages let the compiler fuse the filtering and mapping steps into a single pass.
PHP has no list comprehension syntax. The same result requires either an explicit loop that pushes onto an accumulator array, or a chain of array_map() and array_filter() calls, both of which are statements or nested function calls rather than a single declarative expression, and array_filter() followed by array_map() walks the array twice unless carefully reordered.
<?php
// PHP equivalent of [x * 2 for x in items if x > 0]
$doubled = array_map(
fn ($x) => $x * 2,
array_filter($items, fn ($x) => $x > 0)
);
?>
See also List comprehension in Wikipedia.
Related : array_map(), Generator, Functional Programming
