Misc #15514: Add documentation for implicit array decomposition

• Status: Open
• Assignee: -

[sos4nt (Stefan Schüßler)]

The documentation for Array Decomposition says: "[...] you can decompose an Array during assignment using parenthesis [sic]" and gives an example:

(a, b) = [1, 2]

p a: a, b: b # prints {:a=>1, :b=>2}

But – as we all know – it's also possible without parentheses, i.e.

a, b = [1, 2]

p a: a , b: b #=> {:a=>1, :b=>2}

This also applies to block arguments when yielding multiple values vs. yielding a single array:

def foo
  yield 1, 2
end

def bar
  yield [1, 2]
end

foo { |a, b| p a: a, b: b }
#=> {:a=>1, :b=>2}

bar { |a, b| p a: a, b: b }
#=> {:a=>1, :b=>2}

In both cases, parentheses are optional.

This implicit array decomposition could be quite surprising for newcomers. The documentation should cover it.

[shevegen (Robert A. Heiler)]

Agreed.

[lugray (Lisa Ugray)]

If that's covered (and I agree it should be) it's also worth showing a case where they are not optional:

def baz
  yield [1, 2], 3
end

baz { |a, b, c| p a: a, b: b, c: c }
#=> {:a=>[1, 2], :b=>3, :c=>nil}

baz { |(a, b), c| p a: a, b: b, c: c }
#=> {:a=>1, :b=>2, :c=>3}