From: mame@...
Date: 2019-08-23T00:53:42+00:00
Subject: [ruby-core:94489] [Ruby master Feature#16115] Keyword arguments from method calls or ignore extra hash keys in splat

Issue #16115 has been updated by mame (Yusuke Endoh).


Thank you for proposing ideas.  They are interesting to me.

As you said in your second example, it is only possible in callee side: changing the method definition to accept a dummy `**` argument.

```
def hello(who:, **)
end

hello(who: "world", foo: "bar")
```

It is difficult to do so in the caller side.  (It is theoretically possible by using `Method#parameters`, but it is an evil magic.)


> 1) What if when you passed an object as an argument to a method that only accepts keyword arguments, the methods listed would be called?

I have never thought this.  Very interesting, but it looks a too big semantics change just for solving the problem.

> 2) Or perhaps add some sort of "triple splat" that would either a) do the method calling thing described above or b) do the regular hash splatting like ** but ignore any keys present that are not listed as keyword arguments:

I have never thought this, nethier.  I have never spent time to consider it yet, but as my first impression, it looks a good idea.  I'd like to hear opinions from matz and people.

----------------------------------------
Feature #16115: Keyword arguments from method calls or ignore extra hash keys in splat
https://bugs.ruby-lang.org/issues/16115#change-80924

* Author: kke (Kimmo Lehto)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Just a thought, feel free to insta-close as stupid.

Currently you can do this:

```
def hello(who:)
  puts "Hello, #{who}"
end

opts = { who: 'world' }
hello(who)
```

Or: 

```
def hello(who:, **_extra_opts) # without eating extra args, you get ArgumentError (unknown keyword: foo)
  puts "Hello, #{who}!"
end

hello(**{ who: 'world', foo: 'bar' })
```

Or even this:

```
def hello(_obj = nil, who: _obj&.who || raise(ArgumentError, "missing who:"))
  puts "Hello, #{who}!"
end

hello(OpenStruct.new(who: 'world'))
```

1) What if when you passed an object as an argument to a method that only accepts keyword arguments, the methods listed would be called? Then you could do:

```
require 'ostruct'
ostruct = OpenStruct.new(who: 'world, foo: 'bar')

def hello(who:)
  puts "Hello, #{who}!"
end

hello(ostruct)
```

2) Or perhaps add some sort of "triple splat" that would either a) do the method calling thing described above or b) do the regular hash splatting like `**` but ignore any keys present that are not listed as keyword arguments:

```
require 'ostruct'
ostruct = OpenStruct.new(who: 'world', foo: 'bar')

def hello(who:)
  puts "Hello, #{who}!"
end

# a:  
hello(***ostruct)  # would call ostruct.who to figure out `who:`

# or b: (currently with ** raises ArgumentError (unknown keyword: foo))
hello(***{ who: 'world', foo: 'bar' }) # would ignore any extra keys 
```

I think this could open up some possibilities (or a can of worms). 




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