How to use Proc lamba returned from a method in Ruby

Question

I am unable to use the Proc returned by valid_transaction as argument in the select filter. This is the code I am using.

require 'json'


module Electrum

  class History

    def self.valid_transaction

      lambda { |tx| tx["date"] == "----" }

    end


    def self.list

      JSON::parse `electrum history`

    end


    def self.confirmed

      list.reject { |tx| tx["date"] == "----" }

    end


    def self.unconfirmed

      list.select(&:valid_transaction)

    end

  end

end

Answer 1

You need to remove the colon:

list.select(&valid_transaction)

The & syntax is used to pass a lambda or proc to a method that is expecting a block. That's what you need here.

With a colon, the meaning of that expression is different:

list.select(&:valid_transaction)

is equivalent to this:

list.select { |tx| tx.valid_transaction }

And that’s why you’re code wasn’t working as expected.