A Case for Guard Clauses

One of my pet peeves in programming is that few people use guard clauses. A guard clause is an almost trivial concept that greatly improves readability. Inside a method, handle your special cases right away and return immediately.

Have a look at the following example:

private int doSomething() {
    if (everythingIsGood()) {

        /*
         * Lots and lots of code here, but that's a different story.
         */

        return SOME_VALUE;
    } else {
        return ANOTHER_VALUE;  // a special case
    }
}

You can easily rewrite it using the Replace Nested Conditional with Guard Clauses refactoring from Martin Fowler’s Refactoring:

private int doSomething() {
    if (! everythingIsGood()) // <-- this is your guard clause
        return ANOTHER_VALUE;

    /*
     * Lots and lots of code here, but that's a different story.
     */

    return SOME_VALUE;
}

Once you’ve read past the conditional(s) at the beginning of the method, you know that your world is in order and you don’t have to worry about special cases anymore.

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