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

Visualize your example within a function

def make_user(name)
  user = User.new
  user.username = name
  user.save!
end

There is a big maintenance risk with that approach, basically the implicit return value.

In that code you do depend on save! returning the saved user. But if you use a different duck (or your current one evolves) you might get other stuff like a completion status report. Therefore changes to the duck might break the code, something that would not happen if you ensure the return value with a plain user or use tap.

I have seen accidents like this quite often, specially with functions where the return value is normally not used except for one dark buggy corner.

The implicit return value tends to be one of those things where newbies tend to break things adding new code after the last line without noticing the effect. They do not see what the above code really means:

def make_user(name)
  user = User.new
  user.username = name
  return user.save!       # notice something different now?
end