Reverse traversal

reversed(iterable) is a source for loops and comprehensions over a list, string, bytes, std.bytes.Bytes, or range. It evaluates the source once and visits its elements from last to first, without changing the source order or allocating a reversed copy. Text is traversed by Unicode scalar value, with linear total byte traversal; combining marks remain separate scalars. Ranges retain their element type and original step, including descending and unsigned ranges.

The ordinary iteration ownership rules apply. An owned list transfers its elements and drops its unvisited elements on early exit. reversed(&values) yields shared element references; reversed(&mut values) yields exclusive references for a list. A borrowed temporary source stays alive until the loop scope exits. continue advances backward once, and break, return, and propagation clean up the remaining source and current item. Flat tuple unpacking and comprehensions work as in forward iteration.

Use reversed as an input to enumerate or zip, including borrowed inputs, or as a pipeline source: iter(reversed(&values)). Pipelines have no reversed method. Its own input must be a concrete list, string, byte literal, byte buffer, or range; it cannot reverse enumerate, zip, a generator, or a hash collection. It does not create a stored iterator or dispatch to a user iterator protocol.

There are no free any and all functions. Test boolean items with the pipeline terminals iter(flags).any() and iter(flags).all(), or pass a predicate: iter(values).any(is_negative). reversed may supply their input: iter(reversed(&flags)).all(). A call to any(...) or all(...) that names no user function is an error naming these replacements.

Functions and callable bindings named reversed, any, or all retain their normal call behavior. Imported generic functions and generator bodies can use reversed.