Question

I noticed some interesting use of ||= as below –

Code 1

array_1 ||= begin
    (1..5).to_a.map {|el| el*10}
end
puts array_1.to_s # [10,20,30,40,50]

So I executed its following modified version –

Code 2

array_2 ||= def some_method
    (1..5).to_a.map {|el| el*10}
end
puts array_2 # prints nothing
puts array_2.class # NilClass
puts some_method.to_s # [10,20,30,40,50]

1. Why does array_2 gets initialised to nil?
2. Is it possible to invoke some_method using array_2 object? how?

UPDATE

This is what I did for question 2

array_2 ||= "We've got #{def some_method;(1..5).to_a.map {|el| el*10};end;array_2.send(:some_method)}"
puts array_2 # We've got [10, 20, 30, 40, 50]

Answer 1

The return value of a method definition expression (def) is implementation-defined. Most Ruby implementations simply return nil from a def expression, but Rubinius, for example, returns the compiled code of the method wrapped up in a CompiledMethod object.