Bug #7837

IO.open with three arguments where third argument is bogus reports an arity problem instead of type problem

Added by Thomas Enebo almost 3 years ago. Updated almost 3 years ago.

ruby -v:ruby 2.0.0dev (2013-02-08 trunk 39161) [x86_64-darwin11.4.2] Backport:


I am reporting this against 2.0.rc2 but it also applies to mri 1.9.3. If I run the following one-liner:

mri20 -e 'f = File.open("tmp"); IO.open(f.fileno, "r", :heh)'

I get the error:

-e:1:in `initialize': wrong number of arguments (3 for 1..2) (ArgumentError)

This seems wrong because if I change the third argument to an options hash it works fine. So having an arity of 3 is not a problem for open. It is that :heh is not a hash. I think this should generate a TypeError.


#1 Updated by Eric Hodel almost 3 years ago

  • Category set to core
  • Target version set to next minor

Since Ruby 1.9.3p374 has the same behavior I have marked this for next minor:

$ ruby19 -ve 'f = File.open("tmp"); IO.open(f.fileno, "r", :heh)'
ruby 1.9.3p374 (2013-01-15 revision 38858) [x86_64-darwin12.2.1]
-e:1:in initialize': wrong number of arguments (3 for 1..2) (ArgumentError)
from -e:1:in
from -e:1:in `'


#2 Updated by Nobuyoshi Nakada almost 3 years ago

  • Status changed from Open to Rejected

It's common behavior to keyword arguments,

$ ruby -e 'def foo(a, b, c:1);end' -e 'foo(2,3,42)'
-e:1:in foo': wrong number of arguments (3 for 2) (ArgumentError)
from -e:2:in

The optional argument hash is stripped before arity check, so it's "invisible" as arity.

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