为何需检查Match.Success？遍历Regex匹配时该检查是否冗余？

Great question! Let's break this down clearly:

Yes, that if (m.Success) check is completely redundant in your code. Here's why:

• The Regex.Matches() method returns a MatchCollection that only contains successfully matched Match objects. By design, every entry in this collection is guaranteed to have Success == true—failed matches are never added to the collection at all.
• The collection is built specifically to surface only the results where the regex found a valid match against your input string. There's no scenario where a Match from this collection would have a Success value of false.

Looking at your original code snippet:

var regex = new Regex(pattern);
var matches = regex.Matches(input);
var list = new List<string>();
foreach (Match m in matches) {
    if (m.Success) { // This check is unnecessary
        list.Add(m.Value);
    }
}

You can safely simplify it to remove the redundant check:

var regex = new Regex(pattern);
var matches = regex.Matches(input);
var list = new List<string>();
foreach (Match m in matches) {
    list.Add(m.Value);
}

Or even use LINQ for a more concise version (available in .NET 3.5 and later):

var list = new Regex(pattern).Matches(input)
                             .Cast<Match>()
                             .Select(m => m.Value)
                             .ToList();

Just to clarify when you would need to check Match.Success: This only becomes necessary if you're manually iterating using Match.NextMatch(), like this:

var match = regex.Match(input);
while (match.Success) {
    list.Add(match.Value);
    match = match.NextMatch();
}

Here, NextMatch() can return a failed match once there are no more results to find, so the check is required to terminate the loop properly.

内容的提问来源于stack exchange，提问作者fwend