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Code Examples / Notes » ref.funchandxmontero
You can do some kind of overloading functions in PHP using "function_exists". Let's suppose you want a script to call plugins that are php files and you want the plugins to "override" behaviours that if not overriden are used by default. You might for example write a "mySQL table viewer" which displays a table and it "opens a table", "dumps the header", "dumps row-by-row" and then "closes the table". Let's suppose you want a plugin for "Stocks" which prints negative stocks in red, so you want to override the "dumping row-by-row" to do that behaviour. Instead you do not want to have all the "default behaviour" repeated in the plugin. You may then do the following: 1) Define a default plugin (ex: "default.php" 2) Write all your functions in default.php to open, dump and close, but add them a suffix: open_table_default() dump_header_default() dump_row_default() close_table_default() 3) Call your functions with a wrapper: Insetad of this: open_table() or open_table_default() write this: plugincall("open_table"); 4) Then write a function called plugincall which uses function_exists() to see if you call one or the other function: function plugincall($desired_function_name) { if( function_exists( $desired_function_name)) { //Call the plugin //Note the $ before the name $desired_function_name() } else { $desired_function_name = $desired_function_name . "_default"; if( function_exists($desired_function_name)) { //Call the default //Note the $ before the name $desired_function_name() } else { // Nor the plugin nor the default were defined } } So, now, if the require_once(plugin.php) contains a function called "open_table()", it will be used. Instaed, "open_table_default()" will be used. It's not like overloading functions, but it is very useful to write scripts ampliable by other programmers: If they write a function, it is used, if not, the default is used. See ya! Xavier Montero. php-note-2003-june-18
Xavier's example is rather complicated, and his task would be much more simply accomplished by using classes. Define a base class to do the basic functions open, dump, and close, and create extension classes to override whatever behavior. class foo { function open() { // Default functionality for open() } function dump() { // Default functionality for dump() } function close() { // Default functionality for close() } } class bar extends foo { function open() { // Override functionality of open() } // dump() and close() remain as in class foo } michael dot bommarito
I've developed an easy-to-use hack using these functions to emulate overloaded functions. It's especially handy for constructors and/or C++ style templating. Here's a little example to get you going. This does the trick for most circumstances, and if you need more intelligent parsing, it's not too hard to implement with regex or a more suitable classification scheme. N.B. Note the lack of whitespace between variable types in case strings. class Matrix { ... function Matrix() { $args = func_get_args(); $argmatch = implode(",", array_map('gettype', $args)); switch( $argmatch ) { case 'integer,integer': //initialize m x n matrix break; case 'integer,integer,integer': //initialize m x n matrix with constant c break; case 'integer,integer,float': //initialize m x n matrix with constant c break; case 'array': //initialize from array (2D....) break; case 'array,integer': //intialize from array (1D packed with m rows) break; default: //(void) overload? //error handling? break; } } ... } michael t. mcgrew
An interesting way to use functions is by putting other things than PHP in them, i.e. HTML CSS. This can be useful if you will be using a format for many pages. Yes, the include function can be used also, but by defining them in functions can make them more portable in a way and keep you from having to make many include files. You could use include() when one will be putting big portions of PHP, HTML, and/or CSS and will be using them in many pages. Then you could use PHP, HTML, and/or CSS in a function when it is smaller portions of code and only want it to be on a few pages. I have been using include() for HTML and CSS in my early days of PHP coding, but I will be using functions for that a lot more now. <?php function a() { ?> <style type="text/css"> table { border: 1px dashed black; background: #95EAFE; text-align:left; width:610px; } .linkbar { font-family:sans-serif; line-height:40px; top:1px; text-align:center; width:200px; height:10px; } </style> <?php } ?> Now doing: <?php a(); ?> will return all of the CSS just as if you had wrote it on the actual page, or used include() . The same thing goes for HTML code inside a function. The possibilities are endless... |
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