Guard Clause

• A coding technique

• known as Early Return or Bouncer Pattern

Uses

• A if-else block has return statements can convert to a single guard clause

  if (x < 1) {
    return "Not a natural number";
  } else {
    return " a natural number";
  }

  To

  if (x < 1) {
    return "Not a natural number";
  }
  return " a natural number";

  • Can be used validation for inputs

    • consisting in an early exit of a function based on preconditions check.

    if (isNull(x)) {
        throw new IllegalArguementException();
    }

    • If no return in if statement, can use a blank return:

    void describeEating(Item item) {
      if (!item.isFood) {
        print("Wait, that's not even food!");
      } else {
        if (item.isDelicious) {
          print("Hmm, that was good.");
        } else {
          print("Not bad. Nutritious.");
        }
      }
     }

    to

    void describeEating(Item item) {
      if (!item.isFood) {
        print("Wait, that's not even food!");
        return;
      }
    
      if (item.isDelicious) {
         print("Hmm, that was good.");
      } else {
          print("Not bad. Nutritious.");
      }
    }

Benefits

• makes code more readable

  • reduces indentation of your code and therefore makes your code much easier to read and reason about.

  • reduce size of if statements

• it allows exceptions handling to be placed at the beginning

  • to fail fast

• It improves code, like performance

  • by not exiting early, parts of code does not have to be run (ie http/database calls )

Issues

• Overuse

  • especially with validating arguments for every method.

  • Should only do at edge (api) of code, to reduce polluting codebase

Links

• https://careers.per-angusta.com/blog/common-mistakes-with-guard-clause-pattern/