regex matching but not capturing

[Alex Bryan]

On Thursday, 6 April 2023 at 15:52:16 UTC, Paul wrote:
> My regex is matching but doesnt seem to be capturing.  You may 
> recognize this from the AOC challenges.
>
> file contains...
> **Valve AA has flow rate=0; tunnels lead to valves DD, II, BB**
> **Valve BB has flow rate=13; tunnels lead to valves CC, AA**
> **Valve CC has flow rate=2; tunnels lead to valves DD, BB**
> **... etc**
>
> ```d
> auto s = readText(filename);
> auto ctr = ctRegex!(`Valve ([A-Z]{2}).*=(\d+).+valves(,* 
> [A-Z]{2})+`);
> foreach(c;matchAll(s, ctr)) {
> 	fo.writeln(c);
> }
> ```
>
> produces...
> **["Valve AA has flow rate=0; tunnels lead to valves DD, II, 
> BB", "AA", "0", ", BB"]**
> **["Valve BB has flow rate=13; tunnels lead to valves CC, AA", 
> "BB", "13", ", AA"]**
> **["Valve CC has flow rate=2; tunnels lead to valves DD, BB", 
> "CC", "2", ", BB"]**
>
> what I'm attempting to achieve and expect is, for instance, on 
> the 1st line...
> [....lead to valves DD, II, BB", "AA", "0", **", DD", ", II", 
> ", BB"]**

My understanding browsing the documentation is the matchAll 
returns a range of Captures (struct documented at 
https://dlang.org/phobos/std_regex.html#Captures). In your for 
loop I think c[0] will contain the current full match (current 
line that matches), c[1] will contain the first captured match 
("AA" for first line), c.front[2] will contain "0" for first 
line, etc.

There's probably logic somewhere that decides when a Capture is 
used as an argument to writeln, to just print the full match 
(line that matches) (making writeln(capture) the same as 
writeln(capture[0])