Should switch statements always contain a default clause?

by

Switch cases should almost always have a default case.

Reasons to use a default

1.To ‘catch’ an unexpected value

switch(type)
{
    case 1:
        //something
    case 2:
        //something else
    default:
        // unknown type! based on the language,
        // there should probably be some error-handling
        // here, maybe an exception
}

2. To handle ‘default’ actions, where the cases are for special behavior.

You see this a LOT in menu-driven programs and bash shell scripts. You might also see this when a variable is declared outside the switch-case but not initialized, and each case initializes it to something different. Here the default needs to initialize it too so that down the line code that accesses the variable doesn’t raise an error.

3. To show someone reading your code that you’ve covered that case.

variable = (variable == "value") ? 1 : 2;
switch(variable)
{
    case 1:
        // something
    case 2:
        // something else
    default:
        // will NOT execute because of the line preceding the switch.
}

This was an over-simplified example, but the point is that someone reading the code shouldn’t wonder why variable cannot be something other than 1 or 2.

The only case I can think of to NOT use default is when the switch is checking something where its rather obvious every other alternative can be happily ignored

switch(keystroke)
{
    case 'w':
        // move up
    case 'a':
        // move left
    case 's':
        // move down
    case 'd':
        // move right
    // no default really required here
}

More Related Contents:

  1. Why is default required for a switch on an enum?
  2. Turn if-else-if statement into switch statement in Javascript
  3. Why can’t variables be declared in a switch statement?
  4. Reset CSS display property to default value
  5. What is the relative performance difference of if/else versus switch statement in Java?
  6. Expression inside switch case statement
  7. How to set a Django model field’s default value to a function call / callable (e.g., a date relative to the time of model object creation)
  8. If vs. Switch Speed
  9. What does “default” mean after a class’ function declaration?
  10. Variable’s scope in a switch case [duplicate]
  11. How to use a member variable as a default argument in C++?
  12. Error: Jump to case label in switch statement
  13. Compile and execute a JDK preview feature with Maven
  14. Switch statement: must default be the last case?
  15. Get the default values of table columns in Postgres?
  16. Test for multiple cases in a switch, like an OR (||)
  17. python’s webbrowser launches IE, instead of default browser, on Windows relative path
  18. How to ensure completeness in an enum switch at compile time?
  19. Why does Java switch on contiguous ints appear to run faster with added cases?
  20. Why does the Scala compiler disallow overloaded methods with default arguments?
  21. Why can’t the switch statement be applied to strings?
  22. Kotlin ‘when’ statement vs Java ‘switch’
  23. Switch statement in Swift
  24. What are switch expressions and how are they different from switch statements?
  25. Setting default value for Foreign Key attribute
  26. php switch case statement to handle ranges
  27. MySQL: set field default value to other column
  28. Is it possible to extend a default method implementation of a trait in a struct?
  29. PHP: two values in the case of Switch? [duplicate]
  30. Does a break statement break from a switch/select?

Leave a Comment