add Hash#fetch; close #2134

mrbgems/mruby-hash-ext/mrblib/hash.rb

@@ -13,4 +13,18 @@ class Hash
 
   alias each_pair each
   alias update merge!
+
+  def fetch(key, none=NONE, &block)
+    unless self.key?(key)
+      if block
+        block.call
+      elsif none != NONE
+        none
+      else
+        raise RuntimeError, "Key not found: #{key}"
+      end
+    else
+      self[key]
+    end
+  end
 end

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

@@ -27,3 +27,15 @@ assert('Hash#values_at') do
   h = Hash.new { |hash,k| hash[k] = k }
   assert_equal keys, h.values_at(*keys)
 end
+
+assert('Hash#fetch') do
+  h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
+  assert_equal "feline", h.fetch("cat")
+  assert_equal "mickey", h.fetch("mouse", "mickey")
+  assert_equal "minny", h.fetch("mouse"){"minny"}
+  begin
+    h.fetch("gnu")
+  rescue => e
+    assert_kind_of(StandardError, e);
+  end
+end