hash.c: Add Hash#slice

* hash.c (rb_hash_slice): add Hash#slice [Feature #8499]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60229 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

hash.c

@@ -1324,6 +1324,38 @@ rb_hash_reject(VALUE hash)
     return result;
 }
 
+/*
+ *  call-seq:
+ *     hsh.slice -> a_hash
+ *
+ *  Slices a hash to include only the given keys.
+ *  Returns a hash containing the given keys.
+ *
+ *     h = { "a" => 100, "b" => 200, "c" => 300 }
+ *     h.slice("a")  #=> {"a" => 100}
+ */
+
+static VALUE
+rb_hash_slice(int argc, VALUE *argv, VALUE hash)
+{
+    int i;
+    VALUE key, value, result;
+
+    if (argc == 0 || RHASH_EMPTY_P(hash)) {
+	return rb_hash_new();
+    }
+    result = rb_hash_new_with_size(argc);
+
+    for (i = 0; i < argc; i++) {
+	key = argv[i];
+	value = rb_hash_lookup2(hash, key, Qundef);
+	if (value != Qundef)
+	    rb_hash_aset(result, key, value);
+    }
+
+    return result;
+}
+
 /*
  * call-seq:
  *   hsh.values_at(key, ...)   -> array
@@ -4585,6 +4617,7 @@ Init_Hash(void)
     rb_define_method(rb_cHash, "select!", rb_hash_select_bang, 0);
     rb_define_method(rb_cHash, "reject", rb_hash_reject, 0);
     rb_define_method(rb_cHash, "reject!", rb_hash_reject_bang, 0);
+    rb_define_method(rb_cHash, "slice", rb_hash_slice, -1);
     rb_define_method(rb_cHash, "clear", rb_hash_clear, 0);
     rb_define_method(rb_cHash, "invert", rb_hash_invert, 0);
     rb_define_method(rb_cHash, "update", rb_hash_update, 1);

test/ruby/test_hash.rb

@@ -1006,6 +1006,14 @@ class TestHash < Test::Unit::TestCase
     assert_equal(nil, h.select!{true})
   end
 
+  def test_slice
+    h = @cls[1=>2,3=>4,5=>6]
+    assert_equal({1=>2, 3=>4}, h.slice(1, 3))
+    assert_equal({}, h.slice(7))
+    assert_equal({}, h.slice)
+    assert_equal({}, {}.slice)
+  end
+
   def test_clear2
     assert_equal({}, @cls[1=>2,3=>4,5=>6].clear)
     h = @cls[1=>2,3=>4,5=>6]