PHP中匿名函数的使用技巧

<?php 
function F1(){

    $ok="HelloWorld";

    $a=function() use($ok) {
        echo "$ok";
    };
    $a();
}
F1();
?>

<?php 
function F1(){
    $a=function() {
        echo "HelloWorld";
    };
    $a();
}
F1();
?>

<?php 
function F1(){
    $a=function() {
        echo "HelloWorld";
    };
    return $a;
}
$abc=F1();
$abc();
?>

<?php 
function F1(){

    $a=function($name,$do) {
        echo $name." ".$do." HelloWorld";
    };
    return $a;
}
$abc=F1();
$abc(&#39;张三&#39;,&#39;say&#39;);
?>

<?php 
function F1($UnkownFun){
    $UnkownFun("张三");
}

F1(function ($username){
      echo $username;
});

?>