The difference between PHP closure getting external variables and global keyword declaring variables

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closure

Closures are a common concept, and we can often use them with callback functions to make our code simpler and easier to read.

Closures can be copied to make a function use variables in the parent scope. For example:

$global = 'hello';$bbb = function()use($global){ echo $global. "\n";};$bbb();//output 'hello'

global keyword declaration variable

The global variable declaration also allows the function body to call variables outside the function, but unlike use, the global keyword creates a reference to the external variable with the same name, and changes to variables within the function also scope external variables.

$global = 'hello';$fun = function(){ global $global; $global =' world'; echo $global. "\n";};$fun();//output 'world'

This just creates a reference with the same name and does not change the scope of the original external variable $global, which means that calling it in another function still requires declaration or closure.

$global = 'hello';$fun = function(){ global $global; $global =' world'; echo 'a:'.$ global. "\n";};$ccc = function(){ echo 'b:'.$ global;};$fun()$ccc()/*

output

a: worldNotice: Undefined variable: global in xxxxxxx on line xx*/

A slight change in the code makes it easier to compare closures with global keyword declarations, two ways to access external variables.