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);

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

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))

which is close but doesn't result in an array. Do I need to use matchFirst?

Thanks in advance.

[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.

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