Sequencing Using Lexical Scope

It's useful to use factories when testing models. I like Factory Girl with Rails, but with Mongoose the closest I could find was Factory Lady. It does not come with nearly as many niceties.

In the example code, there's this:

emailCounter = 1

Factory.define 'user', User,
  email    : (cb) -> cb("user#{emailCounter++}@example.com") # lazy attribute
  state    : 'activated'
  password : '123456'

I think that looks terrible, so instead here's a sequence helper:

# fn = (int) -> string
sequence = (fn) ->
  count = 0
  (cb) -> cb fn(count++)

The idea is that the count is lexically scoped within the enclosing "sequence" invocation, and the count is incremented to generate unique strings.

email = sequence (n) -> "user#{n}@example.com"

email console.log for [0..2]

# => [email protected]
# => [email protected]
# => [email protected]

Then this can be used in factory lady definitions:

Factory.define 'user', User,
  email    : email
  state    : 'activated'
  password : '123456'

All in all a simple example of the power of lexical scoping in functional languages.