When interacting with a user, it is important to validate all the user input that is coming in, and decide whether further input is required if the user has failed to provide valid input.

With my TicTacToe game, there are several instances where user input is needed;

1. Decide on game type (Human vs Human, Computer vs Human, etc)
2. Decide on board size
3. Pick move (integer from 1-9 for 3x3 board)

I had coded 1 and 3 first, and initially had two very similar looking methods that had the following algorithm;

while true
    input = get_user_input
    break if valid?(input)
    print invalid input message

When I had written the third method, it was the 3rd strike and refactoring had to be done. The only part of the algorithm that varied for each method was the valid() method, the rest was identical.

In Java 8 I would pass a predicate to perform the validation. In Ruby, blocks seem to be a quick and ideal solution for this kind of refactoring. I want to invoke a method but wrap a piece of functionality into a surrounding algorithm.

I was able to achieve this as follows;

def get_validated_user_input
  while true
    input = get_user_input
    break if yield(input)
    print_invalid_message
  end
  input
end

user_move = get_validated_user_input {|input| move_valid?(input, board)}
board_size = get_validated_user_input {|input| board_size_valid?(input, board_size_options)}

Using blocks for user validation