Feature #14313: Support creating KeyError with receiver and key from Ruby

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[kou (Kouhei Sutou)]

KeyError has readers for error details, receiver and key. They are convenient to process KeyError.

We can set receiver and key to KeyError by rb_key_err_new() in C. But we can't set them in Ruby. Because receiver and key use no @ instance variables.

How about adding KeyError#initialize that accepts receiver and key? Because KeyError is useful in pure Ruby libraries. For example, csv library uses KeyError: https://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/lib/csv.rb?revision=59849&view=markup#l321

def fetch(header, *varargs)
  # ...
  raise KeyError, "key not found: #{header}"
  # ...
end

I want to use KeyError for Hash like objects such as Arrow::Table in Red Arrow.

The attached patch adds KeyError#initialize that behaves as the following:

p KeyError.new.message
# => "KeyError": No change. Keep backward compatibility.

p KeyError.new("Message").message
# => "Message": No change. Keep backward compatibility.

p KeyError.new(receiver: Object.new).receiver
# => The Object instance.

p KeyError.new(key: :unknown_key).key
# => :unknown_key

key_error = KeyError.new(receiver: Object.new, key: :unknown_key)
p key_error.receiver
# => The Object instance.
p key_error.key
# => :unknown_key

key_error = KeyError.new("Message", receiver: Object.new, key: :unknown_key)
p key_error.message
# => "Message"
p key_error.receiver
# => The Object instance.
p key_error.key
# => :unknown_key

[nobu (Nobuyoshi Nakada)]

Also NameError?

[Hanmac (Hans Mackowiak)]

should that also extend to the raise function itself like this?

raise KeyError, "key not found: #{header}", key: :header

or is that already done?

[kou (Kouhei Sutou)]

NameError already supports assigning name:

p NameError.new("message", :x).name # => :x

Ah, did you mention receiver not name?

[kou (Kouhei Sutou)]

Kernel.#raise expects backtrace for the 3rd argument.
If we want to extend the current Kernel.#raise behavior, we should create a new issue instead of discussing in this issue.

[matz (Yukihiro Matsumoto)]

I agree with the original proposal. We are not going to enhance raise behavior (yet).

Matz.

[kou (Kouhei Sutou)]

• Status changed from Open to Closed

Applied in changeset trunk|r62049.

---

KeyError#initialize accepts receiver and key.
[Feature #14313][ruby-core:84626]

[nobu (Nobuyoshi Nakada)]

Shouldn't unspecified attribute raise an exception?

diff --git c/error.c i/error.c
index 990f9f7855..7870e58035 100644
--- c/error.c
+++ i/error.c
@@ -1692,8 +1692,6 @@ key_err_initialize(int argc, VALUE *argv, VALUE self)
 {
     VALUE message;
     VALUE options;
-    VALUE receiver = Qnil;
-    VALUE key = Qnil;
 
     rb_scan_args(argc, argv, "01:", &message, &options);
 
@@ -1711,16 +1709,13 @@ key_err_initialize(int argc, VALUE *argv, VALUE self)
 	keywords[1] = id_key;
 	rb_get_kwargs(options, keywords, 0, 2, values);
 	if (values[0] != Qundef) {
-	    receiver = values[0];
+	    rb_ivar_set(self, id_receiver, values[0]);
 	}
 	if (values[1] != Qundef) {
-	    key = values[1];
+	    rb_ivar_set(self, id_key, values[1]);
 	}
     }
 
-    rb_ivar_set(self, id_receiver, receiver);
-    rb_ivar_set(self, id_key, key);
-
     return self;
 }
 
diff --git c/test/ruby/test_key_error.rb i/test/ruby/test_key_error.rb
index 852bd32712..fe1d5bb5ab 100644
--- c/test/ruby/test_key_error.rb
+++ i/test/ruby/test_key_error.rb
@@ -15,11 +15,15 @@
     receiver = Object.new
     error = KeyError.new(receiver: receiver)
     assert_equal(receiver, error.receiver)
+    error = KeyError.new
+    assert_raise(ArgumentError) {error.receiver}
   end
 
   def test_key
     error = KeyError.new(key: :key)
     assert_equal(:key, error.key)
+    error = KeyError.new
+    assert_raise(ArgumentError) {error.key}
   end
 
   def test_receiver_and_key

[nobu (Nobuyoshi Nakada)]

• Related to Bug #14670: Objectで定義したmethod_missingでsuperが使えない added