UB: C#'s Regex.Match returns whole string instead of part when matching

Question

Attention! This is NOT related to Regex problem, matches the whole string instead of a part

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Hi all. I try to do

Match y = Reg         


        

Answer 1

My test regex was different from any others in the project's scope (thats what happens when Perl guy comes to C#), as it had no lookaheads/lookbehinds. So this discovery took some time.

Now, why we should call Regex behaviour undocumented, not undefined:

let's do some matches against "1.234567890".

• PCRE-like syntax: (.)\.2345678
• lookahead syntax: (.)(?=\.\d)

When you're doing a normal match, the result is copied from whole matched part of line, no matter where you've put the parentesizes; in case of lookaheads present, anything that did not belongs to them is copied.

So, the matches will return:

• PCRE: 1.2345678 (at 2300, this looks like original string and I start yelling here at SO)
• lookahead: 1