How do I test if a replacement string needs to be a regular expression?

Question

I searched ... and searched...I don't mean Can I test if a regex is valid, I want to test if a replacement string needs to be used in Regex.Replace or is a simple String.Replace going to give me the same result, only faster.

ie. for a given string replacement do I need to use

Regex.Replace(input, replacement)

instead of

string.Replace(input, replacement)

This assumes (always a great idea) that string.Replace is faster than Regex.Replace.

edit: yes, a great idea. Not. Regex.IsMatch vs string.Contains for one.

Leaving this here as an example of premature optimization. As with most things in life - "It depends". I think that if you had hundreds or thousands of patterns then it may be worth sifting out the simple ones, depending on the likelihood of there being simple ones. For a manageable number of patterns, just do the Regex.

"I want to test if a replacement string needs to be used in Regex.Replace or is a simple String.Replace going to give me the same result, only faster." HOW? — CAD bloke, Jul 06 '14 at 22:57
Are you asking to figure this our dynamically? IE, I could give you any input string and you want to determine in code, ok choose `string.Replace` and then I give you another string and you determine use `Regex.Replace` because in this instance it's faster? Or are you asking which one is faster (period)? — Prescott, Jul 06 '14 at 22:58
Couldn't you set up some timers and test this pretty easily? — Prescott, Jul 06 '14 at 22:58
@CADbloke *HOW?* is not a question. It implies *write if for me*. Better, you write your test cases and ask here if you get a problem. — I4V, Jul 06 '14 at 23:05
@Prescott Basically I'm looking for the presence if a wildcard-type replacement in the string (eg. `.*` `\d` `[a-z]`) - if there's not wildcard then it's just a simple string.Replace, if there's a wildcard then it is more involved. — CAD bloke, Jul 06 '14 at 23:06
Got it, thanks - I think you've got a reasonable answer then — Prescott, Jul 06 '14 at 23:09
@I4V "How" is a question but your point of it not being a genius-grade question may be valid. I never claimed to be a genius. — CAD bloke, Jul 06 '14 at 23:10
http://meta.stackoverflow.com/questions/251758/why-is-stack-overflow-so-negative-of-late — CAD bloke, Jul 06 '14 at 23:13

score 2 · Accepted Answer · answered Jul 06 '14 at 22:57

You can safely assume that if Regex.Escape(pattern) == pattern then you can use a good old string replacement.

But this is micro-optimization... So do measure whether this actually is worth the additional complexity. I bet the regex engine can figure that out, but I may be wrong: either way, never make assumptions out of thin air in cases like that, but back them up with measures.

How do I test if a replacement string needs to be a regular expression?

1 Answers1