When blocks are more useful than functions (ruby)?

Question

I have two examples that give the same result.

With block:

def self.do_something(object_id)
  self.with_params(object_id) do |params|
    some_stuff(params)
  end
end

def self.with_params(object_id, &block)
  find_object_by_id
  calculate_params_hash
  block.call(params_hash)
end

and with method:

def self.do_something(object_id)
  some_stuff(self.get_params(object_id))
end

def self.get_params(object_id)
  find_object_by_id
  calculate_params_hash
  params_hash
end

The second solution seems more straightforward, but I found some usages of the first one in our application code. My question is: in which situation the first one is recommended? What are the pros and cons of each one?

Answer 1

Normally people use blocks when they want to run a piece of code inside of another piece of code. Examples:

DB.with_shard_for_user(user_id) do |db|
  # perform operations on a user's shard

end # shard is reverted back to original value

File.new(filename) do |file|
  # work with file
end # file is closed automatically

User.transaction do
  # run some operations as a single transaction
end

These blocks are closed on their lexical context (they capture variables from where the block is declared, and carry them over to the place when blocks are called).

Schematic structure of a method that accepts a block.

def transaction
  open_transaction # pre- part

  yield if block_given? # run provided code

  commit_transaction # post- part
rescue
  rollback_transaction # handle problems
end

In your first example, use of a block is probably unjustified (IMHO). Too complex for no apparent reason.