Five Lines of Code

4 Make type codes work

This chapter covers

• Eliminating early binding with Never use if with else and Never use switch
• Removing if statements with Replace type code with classes and Push code into classes
• Removing bad generalization with Specialize method
• Preventing coupling with Only inherit from interfaces
• Removing methods with Inline method and Try delete then compile

At the end of the last chapter, we had just introduced a handleInput function that we could not use Extract method (P3.2.1) on because we did not want to break up the else if chain. Unfortunately, handleInput is not compliant with our fundamental Five lines (R3.1.1) rule, so we cannot leave it as is.

Here’s the function.

Listing 4.1 Initial

function handleInput(input: Input) ...