Challenge 1: Dynamic Dispatch With send — Solution

class Calculator
  def add(a, b)
    a + b
  end

  def subtract(a, b)
    a - b
  end

  def multiply(a, b)
    a * b
  end

  def calculate(operation, a, b)
    return nil unless respond_to?(operation)

    send(operation, a, b)
  end
end

calc = Calculator.new
puts calc.calculate(:add, 4, 5)
puts calc.calculate(:multiply, 3, 6)
puts calc.calculate(:divide, 10, 2).inspect

=begin
Output:
9
18
nil

Notes:
- calculate(operation, a, b) accepts the operation as a symbol and checks
  respond_to?(operation) before attempting to call it at all.
- :divide was never defined on Calculator, so respond_to?(:divide) is
  false, and calculate returns nil immediately instead of raising a
  NoMethodError.
- send(operation, a, b) is only reached once respond_to? has already
  confirmed the method exists, which is the safe, idiomatic way to pair
  the two together.
=end