Ruby 3.0 Keyword and Positional Arguments - TL;DR

I appreciate technical notes.

Here is a summary for posterity (i.e. me in the future.)

Keyword Arguments

# to use keyword arguments do:

foo(k: expr)  # or
foo(**expr)   # double splat

# with the definitions:

def foo(k: default) # or 
def foo(k:) # or 
def foo(**kwargs)

# please don't do this anymore, even though it will work
def foo(kwargs = {})
  kwargs
end

foo(k: 1) #=> {:k=>1}

# please do this instead:

def foo(**kwargs)
  kwargs
end

foo(k: 1) #=> {:k=>1}

Delegation

Must explicitly delegate:

# for ruby 3:

def foo(*args, **kwargs, &block)
  target(*args, **kwargs, &block) 
end

Watch out

  1. If you’re passing non-symbol keys as keyword arguments:
def foo(**kwargs)
  kwargs
end
foo("key" => 42)
  1. Double splat with an empty hash (*{}) ```rb def foo(args) args end

empty_hash = {} foo(**empty_hash) #=> Ruby 2.6 or before: [{}] #=> Ruby 2.7 or later: []



 3. The no-keyword-arguments syntax (**nil) is introduced

```rb
def foo(*args, **nil)
end

foo(k: 1)
  #=> Ruby 2.7 or later: no keywords accepted (ArgumentError)
Written on May 10, 2024