Ruby中已定义方法却提示未定义的问题求助（Mastermind项目）

Hey there! Let's figure out why you're hitting that frustrating NameError when trying to call your check method. I've been in your shoes as a Ruby beginner—mixing up instance vs. class methods is super common, so let's break this down simply.

The Root of the Problem #

That error message tells you exactly what's wrong: you're trying to call check as a class method (directly on the Mastermind class itself, like Mastermind.check), but you defined check, userAnswer, and chooseWord as instance methods (regular methods inside the class without a self. prefix).

Instance methods belong to individual instances of your class (think: a specific game of Mastermind), not the class itself. So you can't call them directly on the class—you need to create an instance of Mastermind first.

How to Fix It #

Let's walk through corrected code with explanations:

Step 1: Define Your Class with Instance Methods

Keep your methods as instance methods (since each game needs its own secret word, user guesses, etc.), but add an initialize method to set up the game when an instance is created:

class Mastermind
  def initialize
    # Set up the game state when a new instance is created
    @secret_word = chooseWord # Call your chooseWord method here
  end

  # Your check method (instance method)
  def check
    user_guess = userAnswer # Call userAnswer to get input
    # Add your logic to compare user_guess with @secret_word here
    puts "Checking your guess: #{user_guess} against secret word: #{@secret_word}"
    # Ruby automatically returns the last line's value, but since you want "no return value",
    # ending with a puts (which returns nil) is totally fine
  end

  # Your userAnswer method (instance method)
  def userAnswer
    puts "Enter your 4-letter guess:"
    gets.chomp.downcase # Clean up user input
  end

  # Your chooseWord method (instance method)
  def chooseWord
    # Example: pick a random secret word from a list
    ["ruby", "code", "game", "play"].sample
  end
end

Step 2: Create an Instance & Call the Method

Instead of calling Mastermind.check, create a new game instance first, then call the method on that instance:

# Create a new Mastermind game instance
my_game = Mastermind.new

# Call the check method on the instance
my_game.check

What If You Accidentally Tried to Call Instance Methods Inside a Class Method? #

If you had a class method (like def self.some_method) and tried to call check inside it, that would also throw the same error—because class methods can't access instance methods directly. For Mastermind, you almost certainly want to use instance methods since each game is a separate instance with its own state.

Quick Note on "No Return Value" Methods #

Ruby doesn't have true "void" methods—every method returns the value of its last line. But if you don't need to use the return value, you don't have to worry about it. Ending your method with a puts or other action will effectively act like a "no return value" method for your purposes.

That should fix the NameError you're seeing! If you run into snags with the game logic itself, feel free to share more of your code and we can troubleshoot further.

内容的提问来源于stack exchange，提问作者llamingo