Issue #8316 has been updated by nobu (Nobuyoshi Nakada). Category set to core Status changed from Open to Assigned Assignee set to mame (Yusuke Endoh) ---------------------------------------- Bug #8316: Can't pass hash to first positional argument; hash interpreted as keyword arguments https://bugs.ruby-lang.org/issues/8316#change-38858 Author: TylerRick (Tyler Rick) Status: Assigned Priority: Normal Assignee: mame (Yusuke Endoh) Category: core Target version: ruby -v: ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-linux] Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN I'm able to pass any other type of object to my first argument: def foo(hash, opt: true) puts "hash: #{hash}, opt: #{opt.inspect}" end foo 'a' # => hash: a, opt: true foo [{a:1}] # => hash: [{:a=>1}], opt: true foo [{a:1}], opt: false # => hash: [{:a=>1}], opt: false But when I try to pass a hash, it raises an ArgumentError: foo({a:1}) # Raises ArgumentError: unknown keyword: a # Expected behavior: hash: {:a=>1}, opt: true I tried to work around the "unknown keyword" error by using ** but ended up getting a "wrong number of arguments (0 for 1)" error instead. def foo_with_extra(hash, **extra) puts "hash: #{hash}, extra: #{extra.inspect}" end foo_with_extra 'a' # hash: a, extra: {} foo_with_extra [{a:1}] # hash: [{:a=>1}], extra: {} foo_with_extra [{a:1}], opt: false # hash: [{:a=>1}], extra: {:opt=>false} foo_with_extra({a:1}) # Raises ArgumentError: wrong number of arguments (0 for 1) # Expected behavior: hash: {:a=>1}, extra: {} This behavior is surprising and I haven't seen it mentioned anywhere before. Is it really intentional? -- http://bugs.ruby-lang.org/