Simulating the switch Statement (ActionScript: The Definitive Guide)

7.4. Simulating the switch Statement

Though switch statements (sometimes called case statements) are not supported by ActionScript, this common form of complex conditional can be emulated. A switch statement lets us execute only one of a series of possible code blocks based on the value of a single test expression. For example, in the following JavaScript switch statement, we greet the user with a custom message depending on the value of the test expression gender:

var surname = "Porter";
var gender = "male";

switch (gender) {   
  case "femaleMarried" :       
    alert("Hello Mrs. " + surname);       
    break;    
  case "femaleGeneric" :      
    alert("Hello Ms. " + surname);  
    break;   
  case "male" :       
    alert("Hello Mr. " + surname);      
    break;    
  default :      
    alert("Hello " + surname); 
}

In the JavaScript example, switch attempts to match the value of gender to one of the case expressions: "femaleMarried", "femaleGeneric", or "male". Because gender matches the expression "male", the substatement alert("Hello Mr. " + surname); is executed. If the test expression had not matched any case, then the default statement -- alert("Hello " + surname); -- would have been executed.

In ActionScript, we can simulate a switch statement using a chain of if-else if-else statements, like this:

var surname = "Porter";
var gender = "male";

if (gender == "femaleMarried") {
  trace("Hello Mrs. " + surname);
} else if (gender == "femaleGeneric") {
  trace("Hello Ms. " + surname);
} else if (gender == "male") {
  trace("Hello Mr. " + surname);
} else {
  trace("Hello " + surname);
}

In a more advanced approach, we could simulate a switch as a series of functions stored in the properties of a generic object. Example 7-1 shows the technique. Pay close attention to the comments to learn how it works. Also note the use of the conditional operator, which we encountered earlier.

Example 7-1. A Simulated switch Statement

var surname = "Porter"; // Our user's name
var gender = "male";    // Our user's gender (the test expression)

// Create an object to act as our simulated switch statement
var mySwitch = new Object( );

// Assign "case expression" properties to the mySwitch object.
// Each "case expression" property holds a function.
mySwitch.femaleMarried = function( ) {
  trace("Hello Mrs. " + surname); 
};
mySwitch.femaleGeneric = function( ) {
  trace("Hello Ms. " + surname); 
};
mySwitch.male = function( ) {
  trace("Hello Mr. " + surname); 
};
mySwitch.default = function( ) {
  trace("Hello " + surname);
};

// Now execute the appropriate function, depending on the
// value of gender (in our case, "male"). If the named
// property doesn't exist, execute the default function instead.
mySwitch[gender] ? mySwitch[gender]() : mySwitch["default"]( );