Ruby block implicit variables

Question

I wonder if Ruby has something like implicit block parameters or wildcards as in Scala that can be bound and used in further execution like this:

my_collection.each { puts _ }

or

my_collection.each { puts }

There's something like symbol to proc that invokes some method on each element from collection like: array_of_strings.each &:downcase, but I don't want to execute object's method in a loop, but execute some function with this object as a parameter:

my_collection.each { my_method(_) }

instead of:

my_collection.each { |f| my_method(f) }

Is there any way to do that in Ruby?

BroiSatse · Accepted Answer · 2014-06-04 13:05:01Z

7

You should be able to do it with:

my_collection.each &method(:my_method)

method is a method defined on Object class returning an instance of Method class. Method instance, similarly to symbols, defines to_proc method, so it can be used with unary & operator. This operator takes a proc or any object defining to_proc method and turns it into a block which is then passed to a method. So if you have a method defined like:

def my_method(a,b)
  puts "#{b}: #{a}"
end

You can write:

[1,2,3,4].each.with_index &:method(:my_method)

Which will translate to:

[1,2,3,4].each.with_index do |a,b|
  puts "#{b}: #{a}"
end

edited Jun 4, 2014 at 13:05

answered Jun 4, 2014 at 12:33

BroiSatse

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1 Comment

Kamil Lelonek Over a year ago

To avoid & interpreted as argument prefix warning add parenthesis around &method like my_collection.each(&method(:my_method))

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