Replace Temp with Query

Move the entire expression to a method and replace references to the temp with calls to the method.

“You are using a temporary variable to hold the result of an expression. Extract the expression into a method.”

Turn variables into functions.

graph LR
    A[Variable] -->|Refactoring| B[Function Call]

When to apply (Smells)

  • Long Method: Temps often force methods to be long because they are only visible locally.
  • Duplicate Logic: The calculation is needed elsewhere.

Motivation

  • Reusability: Logic in a method is reusable; logic in a temp is not.
  • Cleaner scope: Removes local variables, making Extract Method easier.

Mechanics (Steps)

  1. Extract the expression into a new method (it should be side-effect free / pure).
  2. Replace references to the temp with calls to the new method.
  3. Remove the temp.

Explanation

Problem

You place the result of an expression in a local variable for later use.

Solution

Move the entire expression to a separate method and return the result from it. Query the method instead of using a variable.

Real world analogy

Instead of calculating the bill, writing it on a napkin (temp), and carrying the napkin around, you just ask the waiter (query) whenever you need to know the total.

Pros and Cons

Pros Cons
  • Code reuse
  • Reduces detailed logic in method
    		•
  • Possible performance cost (calling method multiple times)
    		•

    Comparison

    • Related: Extract Method.

    Code example

    Typescript

    Before

    After

    PHP

    Before

    After