Question

Is there any difference in speed/memory usage for these two equivalent expressions:

Regex.IsMatch(Message, "1000")

Vs

Message.Contains("1000")

Any situations where one is better than other ?

The context of this question is as follows:
I was making some changes to legacy code which contained the Regex expression to find whether a string is contained within another string. Being legacy code I did not make any changes to that and in the code review somebody suggested that Regex.IsMatch should be replaced by string.Contains. So I was wondering whether the change was worth making.

Answer 1

For simple cases String.Contains will give you better performance but String.Contains will not allow you to do complex pattern matching. Use String.Contains for non-pattern matching scenarios (like the one in your example) and use regular expressions for scenarios in which you need to do more complex pattern matching.

A regular expression has a certain amount of overhead associated with it (expression parsing, compilation, execution, etc.) that a simple method like String.Contains simply does not have which is why String.Contains will outperform a regular expression in examples like yours.