fn byteLengthV(s: String) -> Int64
The s.byteLength field as a function.
std/strpred
10 exports, from std/strpred.vyrn.
The string predicates and slice, written on the byte view (bytes, s[i], stringFromBytes).
Offsets and lengths are bytes. A byte-wise scan is safe on UTF-8: a valid needle starts with an ASCII or a lead byte, so it cannot match at a continuation byte. The functions read the byteLength field, never byteLengthV: the field is O(1) and folds at compile time, while byteLengthV copies the string (4.5 ns against 72.5 ns on 47 bytes). The s.byteLength field as a function.
Dependencies
The import graph shows the whole library.
- Imports
- nothing else in std/
fn startsWith(s: String, needle: String) -> Bool
Does s begin with needle? An empty needle is a prefix of everything.
fn endsWith(s: String, needle: String) -> Bool
Does s end with needle? An empty needle is a suffix of everything.
fn skipTable(needle: String, haystackBytes: Int64) -> Array<UInt32>
Boyer-Moore-Horspool's bad-character table for needle: for each byte, how far a window may jump when it ends on that byte. A plain Array, not a record: a field read per byte costs the interpreter measurably, and an array argument is shared copy-on-write.
fn findPlain(s: String, needle: String, from: Int64 where value >= 0) -> Option<Int64>
The first occurrence of needle at or after from, or None. A found offset is at most s.byteLength - needle.byteLength, so an empty needle occurs at from only when from <= s.byteLength. O(n*m).
fn worthPreparing(needle: String, haystackBytes: Int64) -> Bool
Whether a table for needle pays over a haystack of that size. Callers ask before building the table: std/vyx calls contains on short strings millions of times, and an allocation per call cost it about 10%.
fn findSkipping(s: String, needle: String, from: Int64 where value >= 0, skip: Array<UInt32> where value.length >= 256) -> Option<Int64>
fn contains(s: String, needle: String) -> Bool
Whether needle occurs in s; an empty needle occurs everywhere.
type SliceError = enum { OutOfRange(Int64), SplitsCharacter(Int64) }
The two ways a byte range fails to name a substring, each carrying the offset that failed.
fn slice(s: String, start: Int64, end: Int64) -> Result<String, SliceError>
The bytes of s from start up to end, both byte offsets on UTF-8 character boundaries.
OutOfRange(start) when start < 0; OutOfRange(end) when end > s.byteLength or start > end. SplitsCharacter(i) when cut point i lands on a continuation byte. The range is checked before the boundary, as examples/strpredbytes.vyrn pins. A string that holds NUL, which no program can construct, returns SplitsCharacter(start).
It reads s[i] and s.byteLength, never bytes(s): std/scan slices once per token, so a whole-string copy per call would be quadratic.
Tests
3 test blocks in std/strpred.vyrn. CI runs all of them.
Test names
- the predicates answer the same on ASCII and on multi-byte text
- contains finds an overlapping repeat and a match at the very end
- an empty needle occurs at an offset up to the length and nowhere past it
Examples
11 programs in examples/ import this module. Each runs as WebAssembly and as a native binary.