Help with Regular Expressions (std.regex)

[user1234]

On Sunday, 3 March 2019 at 18:07:57 UTC, Samir wrote:
> I am belatedly working my way through the 2018 edition of the 
> Advent of Code[1] programming challenges using D and am stumped 
> on Problem 3[2].  The challenge requires you to parse a set of 
> lines in the format:
> #99 @ 652,39: 24x23
> #100 @ 61,13: 15x24
> #101 @ 31,646: 16x28
>
> I would like to store each number (match) as an element in an 
> array so that I can refer to them by index.  For example, for 
> the first line:
>
> m = [99, 652, 39, 24, 23]
> assert(m[0] == 99);
> assert(m[1] == 652);
> // ...
> assert(m[4] == 23);
>
> What is the best way to do this?  (I will worry about 
> converting characters to integers later.)
>
> I have the following solution so far based on reading Dmitry 
> Olshansky's article on std.regex[3] and the std.regex 
> documention[4]:
>
> import std.stdio;
> import std.regex;
>
> void main() {
>     auto line    = "#99 @ 652,39: 24x23";
>     auto pattern = regex(r"\d+");
>     auto m       = matchAll(line, pattern);
>     writeln(m);
> }
>
> which results in:
> [["99"], ["652"], ["39"], ["24"], ["23"]]
>
> But this doesn't seem to be an iterable array as changing 
> writeln(m) to writeln(m[0]) yields
> Error: no [] operator overload for type RegexMatch!string
>
> Changing the line to writeln(m.front[0]) yields
> 99
>
> but m.front doesn't allow me to access other elements (i.e. 
> m.front[1]):
> requested submatch number 1 is out of range
> ----------------
> ??:? _d_assert_msg [0x4dc27a]
> ??:? inout pure nothrow @trusted inout(immutable(char)[]) 
> std.regex.Captures!(immutable(char)[]).Captures.opIndex!().opIndex(ulong) [0x4d8d57]
> ??:? _Dmain [0x49ffc8]
>
> I've tried something like
> foreach (m; matchAll(line, pattern))
>         writeln(m.hit);
>
> which is close but doesn't result in an array.  Do I need to 
> use matchFirst?
>
> Thanks in advance.
> Samir
>
> [1] https://adventofcode.com/2018
> [2] https://adventofcode.com/2018/day/3
> [3] https://dlang.org/articles/regular-expression.html
> [4] https://dlang.org/phobos/std_regex.html

Hello, Something like this should work:

   import std.array: array;
   auto allMatches = matchAll(line, pattern).array;

or  // sorry i don't have the regex API in mind

   import std.array: array;
   import std.alogrithm.iteration : map;
   auto allMatches = matchAll(line, pattern).map(a => a.hit).array;


What happened with `writeln` is that it iterates the `matchAll` 
results which is an input range, which is lazy. `.array` stores 
the results in an array.