CODEWITHSUNDEEP
c#delegatesasync-await
Quppa
Quppa

Reputation: 1913

Using async/await with pre-defined delegate signature

Given code like this:

static void A() {
  string input = "abcabcabc";
  string pattern = "a";
  string result = Regex.Replace(input, pattern, match => Evaluator(match));
} 

static string Evaluator(Match match) {
  return "d";
}

Is there any way to use async/await with a delegate like this?

This:

static void B() {
  string input = "abcabcabc";
  string pattern = "a";
  string result = Regex.Replace(input, pattern, async match => await EvaluatorAsync(match));
} 

static async Task<string> EvaluatorAsync(Match match) {
  return "d";
}

...doesn't work - the error message is 'The return type of an async method must be void, Task or Task'.

Upvotes: 2

Views: 857

Answers (1)

NeddySpaghetti
NeddySpaghetti

Reputation: 13495

The third parameter you are passing to Regex.Replace must be of type

[SerializableAttribute]
public delegate string MatchEvaluator(
    Match match
)

you are passing in an async delegate whose return type is Task<string>. You can do 

string result = Regex.Replace(input, pattern, match => EvaluatorAsync(match).Result);

but it will block until the result is available which defeats the purpose and also it can cause a deadlock. As higlighted in this answer Regex searches are CPU bound so async will not help you there. The best you can do is use Task.Run to push the work to a background thread.

Upvotes: 2

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