Regex replace: Transform pattern with a custom function

Question

Let's say I have some text such as this:

[MyAppTerms.TermName1]. [MyAppTerms.TermName2]. 1- [MyAppTerms.TermNameX] 2- ...

I want to replace every occurrence of [MyAppTerms.Whatever] with the result of ReadTerm( "MyAppTerms.Whatever" ), where ReadTerm is a static function which receives a term name and returns the term text for the current language.

Is this feasible using Regex.Replace? (alternatives are welcome). I'm looking into substitution groups but I'm not sure if I can use functions with them.

Mattias Buelens · Accepted Answer · 2013-07-19 14:27:07Z

15

Use the Regex.Replace(String, MatchEvaluator) overload.

static void Main()
{
    string input = "[MyAppTerms.TermName1]. [MyAppTerms.TermName2]. 1- [MyAppTerms.TermNameX] 2";
    Regex regex = new Regex(@"\[MyAppTerms\.([^\]]+)\]");
    string output = regex.Replace(input, new MatchEvaluator(RegexReadTerm));

    Console.WriteLine(output);
}

static string RegexReadTerm(Match m)
{
    // The term name is captured in the first group
    return ReadTerm(m.Groups[1].Value);
}

The pattern \[MyAppTerms\.([^\]]+)\] matches your [MyAppTerms.XXX] tags and captures the XXX in a capture group. This group is then retrieved in your MatchEvaluator delegate and passed to your actual ReadTerm method.

It's even better with lambda expressions (since C# 3.0):

static void Main()
{
    string input = "[MyAppTerms.TermName1]. [MyAppTerms.TermName2]. 1- [MyAppTerms.TermNameX] 2";
    Regex regex = new Regex(@"\[MyAppTerms\.([^\]]+)\]");
    string output = regex.Replace(input, m => ReadTerm(m.Groups[1].Value));

    Console.WriteLine(output);
}

Here, you define the evaluator straight inside the code which uses it (keeping logically connected pieces of code together) while the compiler takes care of constructing that MatchEvaluator delegate.

edited Jul 19, 2013 at 14:27

answered Jul 19, 2013 at 14:11

Mattias Buelens

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3 Comments

Mels Over a year ago

This is a perfect case where a lambda expression gives slightly neater code, IMHO. regex.Replace(input, match => ReadTerm(match));

Mattias Buelens Over a year ago

@Mels Very good point, although you probably want to pass only m.Groups[1].Value to ReadTerm instead of the whole Match. Answer updated.

ErikE Over a year ago

You don't even need that syntax for the lambda. if the function takes one parameter, then you can do this: regex.Replace(input, ReadTerm);

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