advantage of tap method in ruby

Question

I was just reading a blog article and noticed that the author used tap in a snippet something like:

user = User.new.tap do |u|
  u.username = \         


        

Answer 1

Apart from the above answers, I have used tap in stubbing and mocking while writing RSpecs.

Scenario: When I have a complex query to stub and mock with multiple arguments which shouldn't go missed. The alternative here is to use receive_message_chain (but it lacks the details).

# Query
Product
  .joins(:bill)
  .where("products.availability = ?", 1)
  .where("bills.status = ?", "paid")
  .select("products.id", "bills.amount")
  .first

# RSpecs

product_double = double('product')

expect(Product).to receive(:joins).with(:bill).and_return(product_double.tap do |product_scope|
  expect(product_scope).to receive(:where).with("products.availability = ?", 1).and_return(product_scope)
  expect(product_scope).to receive(:where).with("bills.status = ?", "paid").and_return(product_scope)
  expect(product_scope).to receive(:select).with("products.id", "bills.amount").and_return(product_scope)
  expect(product_scope).to receive(:first).and_return({ id: 1, amount: 100 })
end)

# Alternative way by using `receive_message_chain`
expect(Product).to receive_message_chain(:joins, :where, :where, :select).and_return({ id: 1, amount: 100 })