XXXVII. Function Handling Functions

简介

These functions all handle various operations involved in working with functions.

需求

无需外部库文件就可以加入本扩展模块的支持。

安装

这些函数作为 PHP 核心的一部分，无需被安装即可使用。

运行时配置

该扩展模块未定义任何设置指令。

预定义常量

该扩展模块未定义任何常量。

目录
call_user_func_array -- Call a user function given with an array of parameters
call_user_func -- Call a user function given by the first parameter
create_function -- Create an anonymous (lambda-style) function
func_get_arg -- Return an item from the argument list
func_get_args -- Returns an array comprising a function's argument list
func_num_args -- Returns the number of arguments passed to the function
function_exists -- Return TRUE if the given function has been defined
get_defined_functions -- Returns an array of all defined functions
register_shutdown_function -- Register a function for execution on shutdown
register_tick_function -- Register a function for execution on each tick
unregister_tick_function -- De-register a function for execution on each tick

add a note User Contributed Notes
Function Handling Functions

xmontero at dsitelecom dot com
24-Aug-2002 05:49

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.

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