Define an operator for your objects

Learn

Many Ruby operators are methods. The expression left + right calls the + method on left and passes right as its argument, just like left.+(right). Defining def +(other) lets your class give that operator a useful meaning.

Distance#+ combines the meters held by two Distance objects and returns a new Distance. Its reader method lets one object read the other object's meters. The implementation expects another Distance and leaves both operands unchanged. Defining an operator does not change its precedence.

Example

class Distance
  attr_reader :meters
  def initialize(meters)
    @meters = meters
  end
  def +(other)
    Distance.new(meters + other.meters)
  end
end
left = Distance.new(4)
right = Distance.new(6)
total = left + right
p total.meters
p left.meters

Experiment

• Try Compare operator and method calls

  Predict both totals. Replace the operator expression with left.+(right) and check whether it changes the result.

• Try Chain additions

  Predict the total and both original values. Add a fourth Distance to the expression and explain why chaining is possible.

Explore the official manual

• Official Ruby 4.1 development documentation: Methods
• Official Ruby 4.1 development documentation: Operators