NSRegularExpression memory hog

Question

I have been trying to bring down the memory usage of my app, and after profiling it turns out that NSRegularExpression is quite a memory hog.

One of my fistMatchInString calls (the first one?) allocates 1 MB of memory which is never released. And each call to firstMatchInString leaks a "NSConcreteValue" (whatever that is).

Have you experienced the same behavior, and do you know how to get around it? Do you know of good alternatives to NSRegularExpression?

Before you ask: all my regular expression patterns are small and created statically. All strings to match are small as well.

Answer 1

Yes, regular expressions are expensive operations.

From the NSPredicate programming guide, it is said that : "Regular expression matching in particular is an expensive operation" and that "you should therefore perform simple tests before a regular expression".

I let you read the performance section of the predicate programming guide. I don't know if predicate can apply to your case but you might even extract some valuable info from the performance section (located in the "using predicate" chapter)

edit :

Look the regular expression part of this link, he is using a static NSRegularExpression instead of allocate it each time.

from this post, even if it's about python, the "+" seems to be more greedy, so there might be some improvement that can be made in your regex, in the expression itself, some best practices to implement.