mruby-array-ext: add Array#deconstruct for pattern matching

Implement new method for Ruby 2.7+ pattern matching compatibility.
Returns the array itself to enable case/in pattern matching syntax.
Complements Hash#deconstruct_keys for complete pattern matching support.

Co-authored-by: Atlassian Rovo Dev

mrbgems/mruby-array-ext/src/array.c

@@ -1261,6 +1261,31 @@ ary_insert(mrb_state *mrb, mrb_value self)
   return self;
 }
 
+/*
+ *  call-seq:
+ *     ary.deconstruct -> ary
+ *
+ *  Returns the array itself for pattern matching.
+ *
+ *  This method is used by pattern matching to deconstruct arrays.
+ *  It simply returns the array itself, allowing pattern matching
+ *  to work with array elements.
+ *
+ *     a = [1, 2, 3]
+ *     a.deconstruct   #=> [1, 2, 3]
+ *
+ *  Pattern matching usage:
+ *     case [1, 2, 3]
+ *     in [x, y, z]
+ *       # x=1, y=2, z=3
+ *     end
+ */
+static mrb_value
+ary_deconstruct(mrb_state *mrb, mrb_value ary)
+{
+  return ary;
+}
+
 void
 mrb_mruby_array_ext_gem_init(mrb_state* mrb)
 {
@@ -1291,6 +1316,7 @@ mrb_mruby_array_ext_gem_init(mrb_state* mrb)
   mrb_define_method_id(mrb, a, MRB_SYM(__normalize_index), ary_normalize_index, MRB_ARGS_REQ(1));
   mrb_define_method_id(mrb, a, MRB_SYM(__fetch), ary_fetch, MRB_ARGS_REQ(3));
   mrb_define_method_id(mrb, a, MRB_SYM(insert), ary_insert, MRB_ARGS_ARG(1, -1));
+  mrb_define_method_id(mrb, a, MRB_SYM(deconstruct), ary_deconstruct, MRB_ARGS_NONE());
 }
 
 void

mrbgems/mruby-array-ext/test/array.rb

@@ -757,3 +757,29 @@ assert("Array#repeated_permutation") do
   assert_repeated_permutation([[]], a, 0)
   assert_repeated_permutation([], a, -1)
 end
+
+assert("Array#deconstruct") do
+  # Basic functionality - returns self
+  a = [1, 2, 3]
+  result = a.deconstruct
+  assert_equal([1, 2, 3], result)
+  assert_true(result.equal?(a))
+
+  # Empty array
+  b = []
+  result_empty = b.deconstruct
+  assert_equal([], result_empty)
+  assert_true(result_empty.equal?(b))
+
+  # Mixed types
+  c = [1, "hello", :symbol, nil, true]
+  result_mixed = c.deconstruct
+  assert_equal([1, "hello", :symbol, nil, true], result_mixed)
+  assert_true(result_mixed.equal?(c))
+
+  # Nested arrays
+  d = [[1, 2], [3, 4], [5]]
+  result_nested = d.deconstruct
+  assert_equal([[1, 2], [3, 4], [5]], result_nested)
+  assert_true(result_nested.equal?(d))
+end