Why doesn't my ruby method call work? (yield)

Question

I can't figure out why I get this error message when I run my file on the console: no block given (yield) (LocalJumpError)

Here my code:

def block_splitter(array)
  array.partition { |item| yield(item) }
end

beatles = ["John", "Paul", "Ringo", "George"]

puts block_splitter(beatles) do |beatle|
  beatle.start_with?("P")
end

Thanks for your help!

score 1 · Answer 1 · answered Jan 05 '21 at 11:59

1

So there is a problem with missing parentheses. Ruby interpreter allow not to use those, but when You use nested method calls It's better (and sometimes necessary) to use them. To fix it You can do something like this

    puts(block_splitter(beatles) do |beatle| 
        beatle.start_with?("P")
    end)

Or even better

puts(block_splitter(beatles) {|beatle| beatle.start_with?("P")})

answered Jan 05 '21 at 11:59

Karol Ostrowski

74
1
2

Thank you so much, I didn't know about it, it really helped! – raphael-allard Jan 05 '21 at 13:00

score 1 · Accepted Answer · answered Jan 05 '21 at 12:04

It's a whitespace issue. Your problem is in this line:

puts block_splitter(beatles) do |beatle|
  # ...
end

The above code is being interpreted like this:

puts(block_splitter(beatles)) do |beatle|
  # ...
end

I.e. the ruby interpreter thinks that the block is being passed to the puts method, not the block_splitter method.

By assigning a variable and printing the result, you'll see that this works as expected:

result = block_splitter(beatles) do |beatle|
  beatle.start_with?("P")
end

puts result

Or, you can define this as a 1-liner, and the ruby interpreter handles it like you expected:

puts block_splitter(beatles) { |beatle| beatle.start_with?("P") }

Or, you could wrap it in extra brackets:

puts(block_splitter(beatles) do |beatle|
  beatle.start_with?("P")
end)

Thank you for all your explanations, it is much clearer for me now! — raphael-allard, Jan 05 '21 at 13:01

Why doesn't my ruby method call work? (yield)

2 Answers2