PHP 5 in Practice

6. Functions Functions in PHP are generally like functions in most other programming languages: They identify blocks of code that can be referenced over and over again. Hence, PHP functions have many of the same characteristics as other lang...

6.1. Setting Optional Parameters When declaring a function, you may have a parameter that you almost always assign to the same value. You occasionally need to use a different value, though, so you cannot just hard-code the value. PHP provides a so...

6.2. Creating Recursive Functions A recursive function is defined simply as a function that calls itself. (Also falling under the definition would be any group of functions that loop among themselves, such as function A calling function B, which i...

6.3. Calling Functions Using a Function Name Stored in a Variable It is possible to store the name of a function as a string and then to call the function from this. Why would you ever want to use this? Well it allows for the function name to be p...

6.4. Dynamically Creating a Function (Lambda-Style) It is possible in PHP to dynamically create a function and store it in a variable. These functions are often referred to as anonymous functions or Lambda-style functions. (This naming scheme come...

6.5. Using an Array of Functions for Processing The creation of one Lambda function can add great versatility to a script. Now imagine creating a whole array of Lambda functions. Such an array allows for easy, programmatic access to a function. As...

6.6. Passing or Returning a Value by Reference Normally in PHP all arguments are passed by value. This means that when you pass a variable in as one of the functions parameters, you get a copy of that variable's value. This way, if you change th...

6.7. Using an Arbitrary Number of Parameters Default parameters can give you an almost arbitrary list of parameters, although there will always be a limit imposed on how many you declare. There are times when it is useful to allow for any number o...

6.8. Requiring a Parameter to Be a Certain Type PHP 5 has implemented type hinting. Type hinting requires the parameter of your function (or an object's method) to be of a specific type. As of the writing of this book, PHP 5.1 only allows this t...