From: tyler@...
Date: 2018-06-06T01:49:17+00:00
Subject: [ruby-core:87422] [Ruby trunk Bug#8316] Can't pass hash to first positional argument; hash interpreted as keyword arguments

Issue #8316 has been updated by TylerRick (Tyler Rick).


ozydingo (Andrew Schwartz) wrote:
> This is unfortunately still an issue with default values in positional arguments:
> 
> 2.2.2 > def foo(hash={}, opt: true); p hash; p opt; end
>  => :foo
> 2.2.2 > foo({a: 1})
> ArgumentError: unknown keyword: a
> 
> Expected behavior is that foo can be called with a hash argument in the first position without needing to specify the optional keyword args.

Ay! Just ran into this today.

Looks like this case is tracked in #12717 and #11967 but won't be fixed until Ruby 3 (#14183).

I wish there were a good workaround. Best I was able to come up with was:

```
def foo(hash={}, options = {opt: true})
  opt = options[:opt]
  [hash, opt]
end

 > foo({a: 1})
=> [{:a=>1}, true]
 > foo({a: 1}, opt: false)
=> [{:a=>1}, false]
```

----------------------------------------
Bug #8316: Can't pass hash to first positional argument; hash interpreted as keyword arguments
https://bugs.ruby-lang.org/issues/8316#change-72410

* Author: TylerRick (Tyler Rick)
* Status: Closed
* Priority: Normal
* Assignee: mame (Yusuke Endoh)
* Target version: 
* ruby -v: ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin13]
* Backport: 
----------------------------------------
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?



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