Question

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What’s this &block in Ruby? And how does it get passes in a method here?

I dont Understand the &block part, what does it do?

here is an example:

def method_missing(method_name, *args, &block)
  @messages << method_name
  @object.send method_name, *args, &block
end

Answer 1

Blocks give you an opportunity to state a callback to pass on to a method.

The & is key here – like @pst mentioned, it “promotes” the block to a Proc and binds the Proc to the variable with the given name.

With &

def time(&block)
  puts block
end

time
# => nil
time { foo }
# => #<Proc:0x00029bbc>

Without &

def time(block)
  puts block
end

time { foo }
# => ArgumentError: wrong number of arguments (0 for 1)
# Because & isn't included, the method instead expected an arguement,
# but as a block isn't a arguement an error is returned.