Array to String with specific format - arrays

Question

I have a hash like this:
#password_constraints = {
length: 'Must be at least 6 character long.',
contain: [
'one number',
'one lowercase letter',
'one uppercase letter.'
]
}
And I want to write a method that returns an human-readable string built from this hash like this one:
Must be at least 6 character long. Must contain: one number, one lowercase letter and an uppercase letter.
Currently, I have a very verbose method with an each that iterates over the #password_constraints[:contain] array and has several conditions to check if I have to put a ,, or an and or nothing.
But I want almost the same behavior as join(', ') but the last delimiter must be and.
I'm looking for some sort of solution like this one with the special join:
def password_constraints
#password_constraints[:length] << ' Must contain.' << #password_constraints[:contain].join(', ')
end
Is there a way to make this more compact or Ruby-like?

Answer 1

You can use the splat operator to split the array and just check the case if there's only one string:
def message(constraints)
*others, second_last, last = constraints[:contain]
second_last += " and #{last}" unless last.nil?
"#{constraints[:length]} Must contain: #{(others << second_last).join(', ')}"
end
#password_constraints = {
length: 'Must be at least 6 character long.',
contain: [
'one number',
'one lowercase letter',
'one uppercase letter.'
]
}
message(#password_constraints)
# => "Must be at least 6 character long. Must contain: one number, one lowercase letter and one uppercase letter."
# if #password_constraints[:contain] = ['one lowercase letter', 'one uppercase letter.']
message(#password_constraints)
# => "Must be at least 6 character long. Must contain: one lowercase letter and one uppercase letter."
# if #password_constraints[:contain] = ['one lowercase letter']
message(#password_constraints)
# => "Must be at least 6 character long. Must contain: one lowercase letter"

Answer 2

I would use a monkey patch here for succinctness (yeah my join_requirements method could probably look a little nicer).
class Array
def join_requirements
result = ""
self.each do |requirement|
if requirement == self.last
result << "and " << requirement
else
result << requirement + ", "
end
end
result
end
end
Then in your code you just see this:
contain = ['one number','one lowercase letter','one uppercase letter.']
puts contain.join_requirements
# => one number, one lowercase letter, and one uppercase letter.

Answer 3

Here's a fun little shorthand trick in Ruby that you can do with arrays to cut out the need for a verbose join.
def password_constraints
#password_constraints[:length] << ' Must contain.' << #password_constraints[:contain] * ", "
end
The Array class' * operator explicitly checks for a string second operand, then converts to calling join under the covers.