while

A while executes its body as long as its condition is truthy.

  1. while some_condition
  2. do_this
  3. end

The condition is first tested and, if truthy, the body is executed. That is, the body might never be executed.

A while‘s type is always Nil.

Similar to an if, if a while‘s condition is a variable, the variable is guaranteed to not be nil inside the body. If the condition is an var.is_a?(Type) test, var is guaranteed to be of type Type inside the body. And if the condition is a var.responds_to?(:method), var is guaranteed to be of a type that responds to that method.

The type of a variable after a while depends on the type it had before the while and the type it had before leaving the while‘s body:

  1. a = 1
  2. while some_condition
  3. # a : Int32 | String
  4. a = "hello"
  5. # a : String
  6. a.size
  7. end
  8. # a : Int32 | String

Checking the condition at the end of a loop

If you need to execute the body at least once and then check for a breaking condition, you can do this:

  1. while true
  2. do_something
  3. break if some_condition
  4. end

Or use loop, found in the standard library:

  1. loop do
  2. do_something
  3. break if some_condition
  4. end