Add slice method to ENV like Hash#slice

[Feature #14559]

From:    Benoit Tigeot <benoit@hopsandfork.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63188 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

hash.c

@@ -4067,6 +4067,35 @@ env_keep_if(VALUE ehash)
     return envtbl;
 }
 
+/*
+ *  call-seq:
+ *     ENV.slice(*keys) -> a_hash
+ *
+ *  Returns a hash containing only the given keys from ENV and their values.
+ *
+ *     ENV.slice("TERM","HOME")  #=> {"TERM"=>"xterm-256color", "HOME"=>"/Users/rhc"}
+ */
+static VALUE
+env_slice(int argc, VALUE *argv)
+{
+    int i;
+    VALUE key, value, result;
+
+    if (argc == 0) {
+        return rb_hash_new();
+    }
+    result = rb_hash_new_with_size(argc);
+
+    for (i = 0; i < argc; i++) {
+        key = argv[i];
+        value = rb_f_getenv(Qnil, key);
+        if (value != Qnil)
+            rb_hash_aset(result, key, value);
+    }
+
+    return result;
+}
+
 /*
  * call-seq:
  *   ENV.clear
@@ -4749,6 +4778,7 @@ Init_Hash(void)
     rb_define_singleton_method(envtbl, "delete", env_delete_m, 1);
     rb_define_singleton_method(envtbl, "delete_if", env_delete_if, 0);
     rb_define_singleton_method(envtbl, "keep_if", env_keep_if, 0);
+    rb_define_singleton_method(envtbl, "slice", env_slice, -1);
     rb_define_singleton_method(envtbl, "clear", rb_env_clear, 0);
     rb_define_singleton_method(envtbl, "reject", env_reject, 0);
     rb_define_singleton_method(envtbl, "reject!", env_reject_bang, 0);

test/ruby/test_env.rb

@@ -281,6 +281,17 @@ class TestEnv < Test::Unit::TestCase
     end
   end
 
+  def test_slice
+    ENV.clear
+    ENV["foo"] = "bar"
+    ENV["baz"] = "qux"
+    ENV["bar"] = "rab"
+    assert_equal({}, ENV.slice())
+    assert_equal({}, ENV.slice(""))
+    assert_equal({}, ENV.slice("unknown"))
+    assert_equal({"foo"=>"bar", "baz"=>"qux"}, ENV.slice("foo", "baz"))
+  end
+
   def test_clear
     ENV.clear
     assert_equal(0, ENV.size)