PHP function_exists function problem, duplicate definition function

$a=get(1);  //出错,找不到定义echo $a;if(!function_exists("get")){   function get($a){      return "test";   }}

To implement a function, is to detect whether this function has no definition, there is no definition, there is no definition
Function_exists location at end of file, prompt for function definition not found

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$a=get(1);  //出错,找不到定义echo $a;if(!function_exists("get")){   function get($a){      return "test";   }}

To implement a function, is to detect whether this function has no definition, there is no definition, there is no definition
Function_exists location at end of file, prompt for function definition not found

if(!function_exists("get")){   function get($a){      return "test";   }}$a=get(1); // 这不就找到了echo $a;

Recommended methods is_callable , manuals

Interpreting Order Execution:

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