![]() More recently, Roslyn enabled source generators. When the C# compiler was rewritten as the "Roslyn" C# compiler, it exposed object models for the entire compilation pipeline, as well as analyzers. NET 7 introduces a new RegexGenerator source generator. The use of also inhibits the use of RegexOptions.Compiled in certain environments some operating systems don't permit dynamically generated code to be executed, and on such systems, Compiled will become a no-op. RegexOptions.Compiled represents a fundamental tradeoff between overheads on the first use and overheads on every subsequent use. The generated IL further needs to be JIT-compiled on first use leading to even more expense at startup. Not only are all of the same costs paid as for the interpreter, but it then needs to compile that resulting RegexNode tree and generated opcodes/operands into IL, which adds non-trivial expense. The most impactful is that it incurs much more construction cost than using the interpreter. There are several downsides to RegexOptions.Compiled. This special casing and the ability to perform optimizations based on knowledge of the pattern are some of the main reasons for specifying RegexOptions.Compiled yields much faster-matching throughput than does the interpreter. For example, if the pattern contained, the interpreter would see an opcode that said "match the input character at the current position against the set specified in this set description" whereas the compiled IL would contain code that effectively said, "match the input character at the current position against 'a' or 'c'". This IL would essentially do exactly what the interpreter would do, except specialized for the exact pattern being processed. When a match was performed, those DynamicMethods would be invoked. The resulting instructions would be transformed further by the reflection-emit-based compiler into IL instructions that would be written to a few DynamicMethods. When you specify RegexOptions.Compiled, all of the same construction-time work would be performed. ![]() When instantiating a new Regex instance or calling one of the static methods on Regex, the interpreter is the default engine employed. When a match is performed, the interpreter simply walks through those instructions, processing them against the input text. The tree is written into a form that can be interpreted as a series of opcodes and operands that provide instructions to the regex interpreter engine on how to match. The tree is then optimized in various ways, transforming the pattern into a functionally equivalent variation that can be more efficiently executed. The specified pattern is parsed, both to ensure the validity of the pattern and to transform it into an internal tree that represents the parsed regex. When you write new Regex("somepattern"), a few things happen. To learn when source generation is possible, see When to use it. Source generation can help your app start faster, run more quickly and be more trimmable. Notice how each of those regexes are made using regex literals – the ability to create a regular expression by starting and ending your regex with a /.Where possible, use source generated regular expressions instead of compiling regular expressions using the RegexOptions.Compiled option. In the third one we’re looking for “The”, but I’ve modified the regex to be case insensitive so that it matches “the”, “THE”, and so on.In the second one we’re matching the range “a” through “m” only, so it will print “the dog sat on the dog”.In that first regular expression we’re asking for the range of all substrings that match any lowercase alphabetic letter followed by “at”, so that would find the locations of “cat”, “sat”, and “mat”.In case you’re not familiar with regular expressions: Print(message.replacing(/at/, with: "dog")) ![]() Print(message.replacing("cat", with: "dog"))īut the real power of these is that they all accept regular expressions too: print(message.ranges(of: /at/)) To see what’s changing, let’s start simple and work our way up.įirst, we can now draw on a whole bunch of new string methods, like so: let message = "the cat sat on the mat" Put together this is pretty revolutionary for strings in Swift, which have often been quite a sore point when compared to other languages and platforms. SE-0357 adds many new string processing algorithms based on regular expressions.SE-0354 adds the ability co create a regular expression using /./ rather than going through Regex and a string.SE-0351 introduces a result builder-powered DSL for creating regular expressions. ![]() This is actually a whole chain of interlinked proposals, including Paul Hudson 5.7 introduces a whole raft of improvements relating to regular expressions (regexes), and in doing so dramatically improves the way we process strings. ![]()
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