[ruby-core:103764] [Ruby master Feature#17844] Support list of methods to test with respond_to?

Issue #17844 has been updated by svoop (Sven Schwyn).


@byroot You're right of course, I'm so tuned in to keyword arguments. :-) Can be done in Ruby as `def respond_to?(*args)`, but you'd have to check the last args member for type. It might be more ore less ugly in C, I honestly know zilch about C. At least code like `if(flag != Qtrue && flag != Qfalse)` is already present in the Ruby source.

@Eregon I like your `all?` approach a lot, definitely better and more self-explanatory than `reduce`!

----------------------------------------
Feature #17844: Support list of methods to test with respond_to?
https://bugs.ruby-lang.org/issues/17844#change-91875

* Author: svoop (Sven Schwyn)
* Status: Open
* Priority: Normal
----------------------------------------
Not sure whether this is a good idea at all, but I guess it doesn't hurt to put it up for debate.

The preferred way to check e.g. whether an argument is acceptable is by use of `respond_to?`:


```ruby
# Don't
def notify(recipient)
  raise ArgumentError unless recipient.instance_of?(User) || recipient.instance_of?(Follower) 
  ...
end

# Do
def notify(recipient)
  raise ArgumentError unless recipient.respond_to? :email
  ...
end
```

However, sometimes the tested object has to respond to more than one method in order to be acceptable:

```ruby
def notify(recipient)
  raise ArgumentError unless recipient.respond_to?(:email) && recipient.respond_to?(:name)
  ...
end
```

The refactored version doesn't look much nicer:

```ruby
def notify(recipient)
  raise ArgumentError unless %i(email name).reduce(true) do |memo, method| 
    memo &&= recipient.respond_to? method 
  end
  ...
```

The limiting factor here is `respond_to?` which only accepts one method as String or Symbol. How about extending it to accept an Array (of String or Symbol) as well?

```ruby
def notify(recipient)
  raise ArgumentError unless recipient.respond_to? %i(email name)
  ...
```

Even nicer, but more complicated to implement due to the last and optional argument `include_all`:

```ruby
def notify(recipient)
  raise ArgumentError unless recipient.respond_to?(:email, :name)
  ...
```

What do you think?




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