[ruby-core:76045] [Ruby trunk Feature#12482] ArgumentError.new(nil) should give a better description

Issue #12482 has been updated by Martin D端rst.


Eike Dierks wrote:
> OK, that change would break the spec.
> I do understand that breaking the spec something that we rarely want to do.

It's not just that it formally breaks the spec. The documentation says that Exceptions take a *message* as an argument. This essentially means that it's the caller's responsibility to make sure the output is understandable.

Nil is not a message. Ruby is so kind as to stringify 'messages' that are not strings. Stringification of *nil* is "", so that is what you end up with.

> I found a workaround:
>     ArgumentError.new([arg]) # wrap arg in Array to give a better error message when arg is nil
> works for me.

What about ArgumentError.new("nil") ? That would be clearer. But in general, even that isn't very helpful, something like ArgumentError.new("Got nil, but expected ...") would be much more helpful.


----------------------------------------
Feature #12482: ArgumentError.new(nil) should give a better description
https://bugs.ruby-lang.org/issues/12482#change-59248

* Author: Eike Dierks
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
Currently:

~~~ruby
ArgumentError.new(nil)  =>  #<ArgumentError: ArgumentError>
ArgumentError.new(nil).to_s => "ArgumentError"
ArgumentError.new(nil).inspect => "#<ArgumentError: ArgumentError>"

~~~

I want to suggest to change this to "ArgumentError(nil)" instead.

Rational:

For testing arguments, I frequently use:

~~~ruby
raise ArgumentError.new(arg) unless ExpectedClass === arg
~~~

However when arg is nil, this raises "ArgumentError" while raising "ArgumentError(nil)" would be much nicer.

This would differentiate between `ArgumentError.new()` and `ArgumentError.new(nil)`

Suggested changes

It looks like `ArgumentError#initialize` inherits Exception#initialize

I'd like to suggest to differentiate between Exception.new() and Exception.new(nil)

~~~ruby
def Exception.new(msg = :__Exception_msg_arg_undefined___)
  case arg
  when :__Exception_msg_arg_undefined___
    # msg = "ClassName"
  when nil
    # msg = "ClassName(nil)" 
  end
~~~

Impact

I believe this should not break existing code as no code should rely on the string returned.
















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