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Diffstat (limited to 'PERFORMANCE.md')
| -rw-r--r-- | PERFORMANCE.md | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/PERFORMANCE.md b/PERFORMANCE.md index b4aeb89..8cd0d9c 100644 --- a/PERFORMANCE.md +++ b/PERFORMANCE.md @@ -62,9 +62,7 @@ on how your program is structured. Thankfully, the [`lazy_static`](https://crates.io/crates/lazy_static) crate provides an answer that works well: - #[macro_use] extern crate lazy_static; - extern crate regex; - + use lazy_static::lazy_static; use regex::Regex; fn some_helper_function(text: &str) -> bool { @@ -147,9 +145,9 @@ In general, these are ordered from fastest to slowest. `is_match` is fastest because it doesn't actually need to find the start or the end of the leftmost-first match. It can quit immediately after it knows there is a match. For example, given the regex `a+` and the haystack, `aaaaa`, the -search will quit after examing the first byte. +search will quit after examining the first byte. -In constrast, `find` must return both the start and end location of the +In contrast, `find` must return both the start and end location of the leftmost-first match. It can use the DFA matcher for this, but must run it forwards once to find the end of the match *and then run it backwards* to find the start of the match. The two scans and the cost of finding the real end of @@ -198,7 +196,7 @@ a few examples of regexes that get literal prefixes detected: Literals in anchored regexes can also be used for detecting non-matches very quickly. For example, `^foo\w+` and `\w+foo$` may be able to detect a non-match -just by examing the first (or last) three bytes of the haystack. +just by examining the first (or last) three bytes of the haystack. ## Unicode word boundaries may prevent the DFA from being used |