From 2ae1160b3966a65abf74b92eab48e3e0b5d77445 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Thu, 25 Dec 2025 16:17:21 +0900
Subject: [PATCH] mruby-array-ext: add Array#find and Array#rfind

Array#find is an optimized version of Enumerable#find for arrays,
using direct index access instead of each iterator.

Array#rfind finds from the end of the array, returning the first
match when scanning backwards.

Both methods support the ifnone parameter for default values.

Co-authored-by: Claude <noreply@anthropic.com>
---
 mrbgems/mruby-array-ext/mrblib/array.rb | 55 +++++++++++++++++++++
 mrbgems/mruby-array-ext/test/array.rb   | 65 +++++++++++++++++++++++++
 2 files changed, 120 insertions(+)

diff --git a/mrbgems/mruby-array-ext/mrblib/array.rb b/mrbgems/mruby-array-ext/mrblib/array.rb
index ea8de8a81..de3bb0a79 100644
--- a/mrbgems/mruby-array-ext/mrblib/array.rb
+++ b/mrbgems/mruby-array-ext/mrblib/array.rb
@@ -726,4 +726,59 @@ class Array
 
     self
   end
+
+  ##
+  # call-seq:
+  #    ary.find(ifnone = nil) { |elem| block } -> obj or nil
+  #    ary.find(ifnone = nil)                  -> Enumerator
+  #
+  # Returns the first element for which the block returns a true value.
+  # If no element matches and +ifnone+ is given, calls +ifnone+ and
+  # returns its result. Otherwise returns +nil+.
+  #
+  # This is an optimized version of Enumerable#find for arrays.
+  #
+  #    [1, 2, 3, 4].find { |x| x > 2 }        #=> 3
+  #    [1, 2, 3, 4].find { |x| x > 10 }       #=> nil
+  #    [1, 2, 3, 4].find(->{0}) { |x| x > 10 } #=> 0
+  #
+  def find(ifnone=nil, &block)
+    return to_enum(:find, ifnone) unless block
+
+    idx = 0
+    len = self.size
+    while idx < len
+      elem = self[idx]
+      return elem if block.call(elem)
+      idx += 1
+    end
+    ifnone&.call
+  end
+
+  ##
+  # call-seq:
+  #    ary.rfind(ifnone = nil) { |elem| block } -> obj or nil
+  #    ary.rfind(ifnone = nil)                  -> Enumerator
+  #
+  # Returns the last element for which the block returns a true value.
+  # Searches from the end of the array to the beginning.
+  # If no element matches and +ifnone+ is given, calls +ifnone+ and
+  # returns its result. Otherwise returns +nil+.
+  #
+  #    [1, 2, 3, 4, 3].rfind { |x| x == 3 }     #=> 3 (the last one)
+  #    [1, 2, 3, 4].rfind { |x| x > 2 }         #=> 4
+  #    [1, 2, 3, 4].rfind { |x| x > 10 }        #=> nil
+  #    [1, 2, 3, 4].rfind(->{0}) { |x| x > 10 } #=> 0
+  #
+  def rfind(ifnone=nil, &block)
+    return to_enum(:rfind, ifnone) unless block
+
+    idx = self.size - 1
+    while idx >= 0
+      elem = self[idx]
+      return elem if block.call(elem)
+      idx -= 1
+    end
+    ifnone&.call
+  end
 end
diff --git a/mrbgems/mruby-array-ext/test/array.rb b/mrbgems/mruby-array-ext/test/array.rb
index 91a7cdabf..fc175b863 100644
--- a/mrbgems/mruby-array-ext/test/array.rb
+++ b/mrbgems/mruby-array-ext/test/array.rb
@@ -782,3 +782,68 @@ assert("Array#deconstruct") do
   assert_equal([[1, 2], [3, 4], [5]], result_nested)
   assert_true(result_nested.equal?(d))
 end
+
+assert("Array#find") do
+  # Basic find
+  assert_equal 3, [1, 2, 3, 4, 5].find { |x| x > 2 }
+  assert_equal 1, [1, 2, 3, 4, 5].find { |x| x < 2 }
+
+  # No match returns nil
+  assert_nil [1, 2, 3].find { |x| x > 10 }
+
+  # Empty array
+  assert_nil [].find { |x| x > 0 }
+
+  # With ifnone callable
+  assert_equal 0, [1, 2, 3].find(->{ 0 }) { |x| x > 10 }
+  assert_equal "default", [1, 2, 3].find(->{ "default" }) { |x| x > 10 }
+
+  # ifnone not called when match found
+  called = false
+  [1, 2, 3].find(->{ called = true; 0 }) { |x| x == 2 }
+  assert_false called
+
+  # Returns first match
+  assert_equal 2, [1, 2, 2, 3].find { |x| x == 2 }
+
+  # Works with different types
+  assert_equal "b", ["a", "b", "c"].find { |x| x == "b" }
+  assert_equal :bar, [:foo, :bar, :baz].find { |x| x == :bar }
+end
+
+assert("Array#rfind") do
+  # Basic rfind - finds from end (first match scanning backwards)
+  assert_equal 5, [1, 2, 3, 4, 5].rfind { |x| x > 2 }  # 5 is first match from end
+  assert_equal 5, [1, 2, 3, 4, 5].rfind { |x| x > 0 }  # 5 is first match from end
+
+  # Returns last occurrence when duplicates exist
+  a = [1, 2, 3, 2, 1]
+  assert_equal 2, a.rfind { |x| x == 2 }  # finds the 2 at index 3
+
+  # No match returns nil
+  assert_nil [1, 2, 3].rfind { |x| x > 10 }
+
+  # Empty array
+  assert_nil [].rfind { |x| x > 0 }
+
+  # With ifnone callable
+  assert_equal 0, [1, 2, 3].rfind(->{ 0 }) { |x| x > 10 }
+  assert_equal "default", [1, 2, 3].rfind(->{ "default" }) { |x| x > 10 }
+
+  # ifnone not called when match found
+  called = false
+  [1, 2, 3].rfind(->{ called = true; 0 }) { |x| x == 2 }
+  assert_false called
+
+  # Compare find vs rfind - same result for unique match
+  arr = [1, 2, 3, 4, 3, 2, 1]
+  assert_equal 3, arr.find { |x| x == 3 }   # first 3 (index 2)
+  assert_equal 3, arr.rfind { |x| x == 3 }  # last 3 (index 4), same value
+
+  # Different results with inequality - rfind scans from end
+  assert_equal 3, arr.find { |x| x >= 3 }   # first >= 3 is 3 (at index 2)
+  assert_equal 3, arr.rfind { |x| x >= 3 }  # scanning from end: 1,2,3 - 3 matches first
+
+  # Works with different types
+  assert_equal "b", ["a", "b", "c", "b", "a"].rfind { |x| x > "a" }  # scanning from end: a,b - b matches
+end