Ruby: Yielding from an inner block does not work

Question

I am working on a Ruby project that outputs text where I want to allow other code to change part of the wrapper. Below is a simplified example:

• Outer wrappers of the output are generated by this project
• Inner wrapper is generated by user-specified code
• Inside this inner wrapper, calling yield will make the project generate the inner contents.

However, I get a very strange error when attempting to run the following code:

def wrapper(&block)
  puts "begin outer wrapper"
  block.call do
    puts "inner content"
  end
  puts "end outer wrapper"
end

wrapper do
  puts "begin inner wrapper"
  yield
  puts "end inner wrapper"
end

I would expect the following output:

begin outer wrapper
begin inner wrapper
inner content
end inner wrapper
end outer wrapper

This does not happen. Instead, Ruby throws the following error: LocalJumpError: no block given (yield)

What is going wrong?

EDIT: Based on @JörgWMittag's answer, this is a variant that does work:

def wrapper(&block)
  puts "begin outer wrapper"
  block.call do
    puts "inner content"
  end
  puts "end outer wrapper"
end

wrapper do |&inner_block|
  puts "begin inner wrapper"
  inner_block.call
  puts "end inner wrapper"
end

Basically, yield and Proc#call() are very different beasts after all.

Answer 1

What is going wrong?

yield transfers control to the block that was passed to the method in whose definition the yield appears. In your case, the yield doesn't appear in a method definition, ergo, there is nowhere to yield to.