Borrowed Text

The compiler-checked str module contract is the sole authority for exact public declarations. Owned UTF-8 storage belongs to String; this module owns borrowed byte-oriented search, validated views, iteration, and owned results derived from str.

Search and range indices are UTF-8 byte offsets. get_range returns none when start > end, an endpoint is outside the input, or an endpoint divides a UTF-8 encoding. Empty ranges and the full input range are valid. The result borrows self; it never reconstructs provenance from an integer address.

strip_prefix and strip_suffix compare exact UTF-8 bytes and return a view into self. The affix is an input to comparison, not a storage origin of the returned view. An empty affix matches and returns the complete input.

split_once finds the first exact separator and returns the borrowed prefix and suffix around it. The separator is excluded from both positions. An empty separator returns the empty view at the start followed by the complete input; a missing separator returns none. Both returned views borrow only self, and the operation performs no allocation.

ASCII whitespace is exactly space (0x20), horizontal tab (0x09), line feed (0x0A), vertical tab (0x0B), form feed (0x0C), and carriage return (0x0D). ASCII trimming removes matching bytes only from the named edges and returns the largest remaining borrowed view. It performs no allocation and does not apply Unicode property tables or normalization. An all-whitespace input returns the empty view positioned at the end of the input and still borrows that input.

split_views rejects an empty separator with std.str.empty_separator. Otherwise it yields the same component boundaries as owned split, including empty components for empty input, adjacent separators, and leading or trailing separators. SplitIter retains both text and separator while it can advance. Each yielded component is a borrowed &str in source order.

lines recognizes LF and CRLF terminators. It omits each terminator, removes CR only immediately before LF, preserves every other CR, yields no item for empty input, and does not add an empty item after a final terminator. LinesIter retains its input and allocates no storage.

repeat concatenates the complete input count times. Zero repetitions or empty input produce an empty owned string. The operation checks complete required capacity before mutation and never wraps an unrepresentable size.

replace_all rejects an empty pattern with std.str.empty_pattern. It scans left to right, replaces non-overlapping matches, and resumes after each complete pattern. Replacement text is copied verbatim and is not searched recursively. A missing pattern produces an independent copy of the input. The result is always well-formed owned UTF-8.

str defines exact byte equality and lexical strict ordering once. String reaches those operations through readonly coercion and does not duplicate their algorithms. Unicode scalar properties and transformations are defined by Unicode Text and Scalars.