[php] cmd

---
>php --version
PHP 7.4.16 (cli) (built: Mar  2 2021 14:06:15) ( ZTS Visual C++ 2017 x64 )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies

>composer --version
Composer version 2.2.5 2022-01-21 17:25:52
---

# base
cgi (common gateway interface) => php-cgi
fastcgi (fast common gateway interface) => php-fpm (fastcgi process manager)
php.exe
php-cgi.exe
php-win.exe
=> ref: https://www.bilibili.com/video/BV1ra4y1L7Wn
=> ref: https://www.itread01.com/content/1543133893.html
=> ref: https://cloud.tencent.com/developer/news/678417

# php
php --version
php --ini
php -h // help
php -a // run as interactive shell
php -i // show php information (<=> builtin function phpinfo())
php -m // show php modules (aka. extensions)
php <file.php>
php -l <file.php> // syntax check only (lint)

# composer
composer --version
composer --help // <=> composer help
composer <command> [options] [arguments]
composer list -h
composer list // list all commands
composer init -h // <=> composer help init
composer global require <package>
composer global remove <package>
composer global show
composer install // install dependencies by composer.json "require" (this will create "vendor" folder)
composer run <script> // run script by composer.json "scripts"
composer require <package>
composer remove <package>

# [note] how to install php + composer
- php
https://windows.php.net/download/
- composer
https://getcomposer.org/download/

IMPORTANT:
1. php is written by c language
2. composer requires that you have php already installed

# [note] ?> vs. ;
see 'end.php'
=> ref: https://www.bilibili.com/video/BV18x411H7qD?p=17

# [note] php include vs. require
include: if the target file is not found, then warning
require: if the target file is not found, then error

IMPORTANT: include vs. include_once
include: do every time
include_once: do only when first time

IMPORTANT: using relative path

|- a1.php               // include './xx/b1.php'
|- xx
    |- b1.php           // include './yy/c1.php'
    |- yy
        |- c1. php
        
php a1.php // something wrong

|- a1.php               // include './xx/b1.php'
|- xx
    |- b1.php           // include './xx/yy/c1.php' // IMPORTANT
    |- yy
        |- c1. php
        
php a1.php // work

IMPORTANT: using return

|- a1.php               // $b1 = include './xx/b1.php' // 100
|- xx
    |- b1.php           // return 100

php a1.php // work

# [note] php use (like python import)
TODO
=> ref: https://jaceju.net/php-include-path/
=> ref: http://justericgg.logdown.com/posts/196891-php-series-autoload

# [note] type hint with nullable
=> ref: https://www.php.net/manual/en/migration71.new-features.php

# [note] how to create lumen project
composer global require laravel/installer // for laravel
composer global require laravel/lumen-installer // for lumen
lumen --version // version of Lumen Installer
lumen new <project-name>
composer create-project --prefer-dist laravel/lumen <project-name>
php artisan --version // version of Lumen
php artisan // show usage of Lumen

# [note] how to run lumen project
cd <project-name>
php -S localhost:8000 -t public

-S <addr>:<port> run with built-in web server
-t <docroot>     specify document root <docroot> for built-in web server

# [note] php shell (enter by php -a)
echo 100; // ; needs
function a() {echo 200;} // cannot redeclare
a();
exit

# [note] how to debug php in vscode
step1. php install "xdeubg.dll" // use https://xdebug.org/wizard
step2. setting xdeubg in php.ini // some settings are different from xdebug v2 and v3
step3. vscode install "PHP Debug"
step4. start server in cmd
step5. start xdebug in vscode
=> ref: https://www.facebook.com/photo.php?fbid=4373264436058581
=> ref: https://dotblogs.com.tw/ianchiu28/2017/06/15/180900

# [note] how to debug php in phpstorm
=> ref: https://jsnwork.kiiuo.com/archives/3079/php-phpstorm-%E8%A8%AD%E5%AE%9A-debug/

# [note] phpstorm recommended theme (vscode dark theme)
=> ref: https://plugins.jetbrains.com/plugin/12255-visual-studio-code-dark-plus-theme

# [note] phpstorm change current line color
step1. Settings | Editor | Color Scheme | General
step2. Editor | Caret row
step3. #04352f
=> ref: https://intellij-support.jetbrains.com/hc/en-us/community/posts/206335019-Change-current-line-highlight

# [note] phpstorm code inspection
Required parameter 'xxx' missing
Expected parameter of type 'xxx', 'int' provided
=> ref: https://www.jetbrains.com/help/phpstorm/php-parameter-type.html

Method call is provided 2 parameters, but the method signature uses 1 parameters
=> ref: https://www.jetbrains.com/help/phpstorm/php-parameters-number-mismatch-declaration.html

Property 'xxx' not found in yyy
=> ref: https://www.jetbrains.com/help/phpstorm/php-undefined-property.html

# [note] phpstorm add datasource and dialect
=> ref: https://www.jetbrains.com/help/idea/database-tool-window.html
=> ref: https://www.jetbrains.com/help/phpstorm/settings-languages-sql-dialects.html

# [note] phpstorm convert table to class (.php)
=> ref: https://blog.jetbrains.com/datagrip/2018/02/13/generate-pojos/
=> ref: https://www.cnblogs.com/jiangfeilong/p/11253449.html

# [note] phpstorm activation code
=> ref: https://gist.github.com/shahadul878/5f33b90e55c1655aee05fa239ec1b978

# [note] learn
=> ref: https://www.youtube.com/watch?v=rFDcGBO4PWc&list=PL2SrkGHjnWcyOquWJIEd7AYAJGMAUdp-a
=> ref: https://www.bilibili.com/video/BV18x411H7qD

_0 common.php

<?php
  
  echo date('Y-m-d H:i:s'), PHP_EOL;
  echo time(), PHP_EOL;
  echo microtime(), PHP_EOL;
  echo strtotime('now'), PHP_EOL;
  echo strtotime('today'), PHP_EOL;
  
  // --------------------------------------------------------

  echo function_exists('func'), PHP_EOL; // 1

  func(100, 200, 300);

  function func($a, $b) {
    // no need echo
    var_dump(func_get_arg(0)); // int(100)
    var_dump(func_get_arg(1)); // int(200)
    var_dump(func_get_arg(2)); // int(300)
    // var_dump(func_get_arg(3)); // warning: func_get_arg():  argument 3 not passed to function
    var_dump(func_get_args()); // array(3) { [0]=>int(100), [1]=>int(200), [2]=>int(300) }
    var_dump(func_num_args()); // int(3)
  }

_a end.php

<?php
  echo 100; // ; cannot be omitted
  echo 200; // ; can be omtted if
            //      1. this line is last
            // and  2. there is the ?>

?> // if ?> is omtted
   // then the following will be treated as php code

// shortcoming:
// if ?> isn't omtted, then
// this line will be output
// this line will be output
// this line will be output

_b variable.php

<?php

  // 1. Built-in Variables
  $GLOBALS
  $_ENV
  $_GET
  $_POST
  $_REQUEST
  $_SERVER
  $_SESSION
  $_COOKIE
  $_FILES

  // 2. Variable Variables
  $a = 'b';
  $b = 100;
  echo $$a; // 100

  // 3. Pass by Value or Reference
  $p = 10;
  $q = $p;
  $q = 20;
  echo $p, ' ', $q;

  $p = 10;
  $q = &$p; // IMPORTANT
  $q = 20;
  echo $p, ' ', $q;

  $p = ['name' => 'peter'];
  $q = $p; // https://stackoverflow.com/questions/2030906/are-arrays-in-php-copied-as-value-or-as-reference-to-new-variables-and-when-pas
  $q['name'] = 'kang';
  echo var_dump($p), ' ', var_dump($q);

_c constant.php

<?php
  
  // 1. Built-in Constants
  PHP_VERSION
  PHP_INT_SIZE
  PHP_INT_MAX
  PHP_EOL
  
  // Magic Constants
  // Def: user cannot change them, but they can be changed by different environments
  __DIR__
  __FILE__
  __LINE__
  __NAMESPACE__
  __CLASS__
  __METHOD__
  __FUNCTION__
    
  // 2. Declare and Use
  define('A1', 100);
  const A2 = 200; // no need $

  echo A1, ' ', A2, PHP_EOL;
  echo constant('A1'), PHP_EOL;
  echo constant('A2'), PHP_EOL;

_d datatype.php

<?php

  // 1. base
  integer
  float
  string
  boolean

  // 2. complex
  object
  array

  // 3. special
  resource
  null
    
  // the following type only be used in manual
  callable
  mixed
  number
    
  // exercise
  $a = 'a1';
  $b = '1.2.3';  
  echo (int)$a, ' ', (int)$b, PHP_EOL;
  echo (float)$a, ' ', (float)$b, PHP_EOL;

  $a = true;
  $b = false;
  echo $a, PHP_EOL; // 1
  echo var_dump($a); // bool(true)
  echo $b, PHP_EOL; //
  echo var_dump($b); // bool(false)

  $a = null;
  echo $a, PHP_EOL; //
  echo var_dump($a); // NULL

  $a;
  echo $a; // notice: undefined variable: a
  echo var_dump($a); // notice: undefined variable: a
                     // NULL

  $a = '100';
  echo var_dump((float) $a); // float(100)
  echo var_dump((double) $a); // float(100)

  $a = '100';
  $b = (float) $a;
  $c = (double) $a;
  $d = 100;
  $e = array();
  $f = true;
  echo gettype($a), PHP_EOL; // string
  echo gettype($b), PHP_EOL; // double
  echo gettype($c), PHP_EOL; // double
  echo gettype($d), PHP_EOL; // integer
  echo gettype($e), PHP_EOL; // array
  echo gettype($f), PHP_EOL; // boolean
  settype($a, 'float');
  echo gettype($a), PHP_EOL; // double
  
  $a = 0b111; // BIN (binary)
  $b = 0111; // OCT (octal)
  $c = 111; // DEC (decimal)
  $d = 0x111; // HEX (hexadecimal)
  echo $a, PHP_EOF;
  echo $b, PHP_EOF;
  echo $c, PHP_EOF;
  echo $d, PHP_EOF;

  $a = PHP_INT_MAX;
  $b = PHP_INT_MAX + 1;
  echo var_dump($a, $b); // $b is float

  $a = 0.7;
  $b = 2.1 / 3;
  echo var_dump($a === $b); // bool(false)

  $a = 100;
  $b = '100';
  echo var_dump($a == $b); // bool(true)
  echo var_dump($a === $b); // bool(false)

  $a = true . '100';
  $b = false . '100';
  $c = null . '100';
  $d = 1234 . '100';
  $e = 1234;
  $e .= '100';
  echo $a, PHP_EOL; // '1100'
  echo $b, PHP_EOL; // '100'
  echo $c, PHP_EOL; // '100'
  echo $d, PHP_EOL; // '1234100'
  echo $e, PHP_EOL; // '1234100'

  $a = 100;
  $b = $a > 100 ? 1 : 0;
  echo $b; // 0
  
  $a = ['peter', 'kang'];
  $b = ['name' => 'peter', 'age' => 27];
  echo var_dump($a); // array(2) { [0] => string(5) "peter" [1] => string(4) "kang" }
  echo var_dump($b); // array(2) { ["name"] => string(5) "peter" ["age"] => int(27) }

_e error.php

<?php
  
  E_ERROR
  E_WARNING
  E_PARSE
  E_NOTICE
  E_CORE_ERROR
  E_CORE_WARNING
  E_COMPILE_ERROR
  E_COMPILE_WARNING
  E_USER_ERROR
  E_USER_WARNING
  E_USER_NOTICE
  E_STRICT
  E_RECOVERABLE_ERROR
  E_DEPRECATED
  E_USER_DEPRECATED
  E_ALL
  => ref: https://www.php.net/manual/en/errorfunc.constants.php

  IMPORTANT:
  You may use these constant names in php.ini but not outside of PHP, like in httpd.conf, where you'd use the bitmask values instead.

  IMPORTANT:
  in php.ini-development,
    error_reporting = E_ALL
    display_errors = On
    log_errors = On
    ;error_log = ...

  IMPORTANT:
  there are two ways to edit config
  1. edit php.ini
  2. run xxx.php
       ini_set(key, value);

  // --------------------------------------------------------

  // trigger_error(string $message, int $error_level = E_USER_NOTICE): bool
  // generates a 'user-level' error/warning/notice message

  trigger_error('Wrong A...');
  echo 100, PHP_EOL;

  trigger_error('Wrong B...', E_USER_ERROR);
  echo 200, PHP_EOL;

_e exception.php

<?php

  try {
    echo 100, PHP_EOL;
    throw new Exception('xxx'); 
    echo 200, PHP_EOL;
  }
  catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), PHP_EOL;
    var_dump($e);
    print_r($e);
  }

  // --------------------------------------------------------

  try {
    1  / 0;
  }
  catch (Error | Exception $e) {
    echo 'Go Here', PHP_EOL; // not reached
    print_r($e);
  }

_f string.php

<?php
	
  $name = 'peter';
  $a = 'Hi $name';
  $b = "Hi $name";
  // $c = "Hi $name2"; // notice: undefined variable: name2
  $d = "Hi {$name}"; // work

  echo $a, PHP_EOL; // Hi $name
  echo $b, PHP_EOL; // Hi peter
  echo $d, PHP_EOL; // Hi peter

  // --------------------------------------------------------

  $name = 'peter';

  $a = <<<'NOW'
    I'm $name
NOW;

  $b = <<<HERE
    I'm $name
HERE;

  $c = <<<HERE
    // a comment
    I'm $name
HERE;

  echo $a, PHP_EOL; // Hi $name
  echo $b, PHP_EOL; // Hi peter
  echo $c, PHP_EOL; // // a comment
                    // Hi peter

  /*
  IMPORTANT:
  1. <<<KEY cannot have any spaces or letters after it
  2. KEY cannot have any spaces or letters before it
  */

  // --------------------------------------------------------

  $a = 'peter';
  $b = '彼得';

  echo strlen($a), PHP_EOL; // 5
  echo strlen($b), PHP_EOL; // 6

  echo mb_strlen($a), PHP_EOL; // 5
  echo mb_strlen($b), PHP_EOL; // 2
  echo mb_strlen($b, 'ASCII'), PHP_EOL; // 6

  /*
  IMPORTANT: php.ini
  1. extension_dir = "ext"
  2. extension=mbstring
  */

  // --------------------------------------------------------

  $arr = ['peter', 'kang'];
  echo implode($arr), PHP_EOL; // peterkang
  echo implode('-', $arr), PHP_EOL; // peter-kang

  $arr = explode('/', '01/28');
  var_dump($arr); // array(2) { [0] => string(2) "01" [1] => string(2) "28" }

  $arr1 = str_split('May');
  $arr2 = str_split('May', 2);
  var_dump($arr1); // array(3) { [0] => string(1) "M" [1] => string(1) "a" [2] => string(1) "y" }
  var_dump($arr2); // array(2) { [0] => string(1) "Ma" [1] => string(1) "y" }

  // --------------------------------------------------------

  $a = ' Hello World ';
  $b = 'Hello World';
  var_dump($a); // string(13) " Hello World "
  var_dump($b); // string(11) "Hello World"
  var_dump(trim($a)); // string(11) "Hello World"
  var_dump(trim($b)); // string(11) "Hello World"
  var_dump(trim($a, 'Hdle')); // string(13) " Hello World "
  var_dump(trim($a, 'HdWr')); // string(13) " Hello World "
  var_dump(trim($b, 'Hdle')); // string(5) "o Wor"
  var_dump(trim($b, 'HdWr')); // string(9) "ello Worl"

  $a = '01234c56c789';
  echo substr($a, 3), PHP_EOL; // 34c56c789
  echo substr($a, 3, 2), PHP_EOL; // 34
  echo strstr($a, 'c'), PHP_EOL; // c56c789
  
  // --------------------------------------------------------

  $a = 'abCdefGhIJ';
  echo strtoupper($a), PHP_EOL; // ABCDEFGHIJ
  echo strtolower($a), PHP_EOL; // abcdefghij
  echo ucfirst($a), PHP_EOL; // AbCdefGhIJ

  // --------------------------------------------------------

  $a = 'abcdefabcdef';
  var_dump(str_replace('f', 'X', $a)); // string(12) "abcdeXabcdeX"
  var_dump($a); // string(12) "abcdefabcdef"

  // --------------------------------------------------------

  $a = 'abcdefabcdef';
  var_dump(strpos($a, 'a')); // int(0)
  var_dump(strpos($a, 'b')); // int(1)
  var_dump(strpos($a, 'g')); // bool(false)
  var_dump(strrpos($a, 'a')); // int(6)

  /*
  IMPORTANT:
  This function may return Boolean false, but may also return a non-Boolean value which evaluates to false.
  Please use the === operator for testing the return value of this function.
  */

  // --------------------------------------------------------

  $a = 'abcdef';
  var_dump(str_repeat($a, 3));
  var_dump(str_shuffle($a));

_g array.php

<?php
  
  PHP 數組
  1. "下標"可以為"整數"或"字符串"
     若下標皆為整數，則稱"索引數組"
     若下標皆為字符串，則稱"關連數組"
     若下標有整數和字符串，則稱"混合數組"
  2. "元素"的順序以"放入順序"為主 (與下標無關)
  3. 元素的類型無限制
  4. 整數下標有"自增特性"
  5. 特殊值下標會"自動轉換"

  // --------------------------------------------------------

  $arr1 = array('peter', 'kang');
  $arr2 = ['peter', 'kang'];
  $arr3[] = 'peter';
  $arr3[] = 'kang';
  $arr4[5] = 'peter';
  $arr5[5] = 'peter';
  $arr5['age'] = 27;

  var_dump($arr1); // array(2) { [0] => string(5) "peter" [1] => string(4) "kang" }
  var_dump($arr2); // array(2) { [0] => string(5) "peter" [1] => string(4) "kang" }
  var_dump($arr3); // array(2) { [0] => string(5) "peter" [1] => string(4) "kang" }
  var_dump($arr4); // array(1) { [5] => string(5) }
  var_dump($arr5); // array(2) { [5] => string(5) "peter" ["age"] => int(27) }

  // --------------------------------------------------------

  $arr1 = array('name' => 'peter');
  $arr2 = ['name' => 'peter'];
  $arr3['name'] = 'peter';
  
  var_dump($arr1); // array(1) { ["name"] => string(5) "peter" }
  var_dump($arr2); // array(1) { ["name"] => string(5) "peter" }
  var_dump($arr3); // array(1) { ["name"] => string(5) "peter" }

  // --------------------------------------------------------

  $arr = 100;
  $arr[] = 200; // warning: cannot use a scalar value as an array

  // --------------------------------------------------------

  $arr[] = 1;
  $arr[10] = 2;
  $arr[] = 3;
  $arr['xx'] = 4;
  $arr[] = 5;
  $arr[3.14] = 6;
  $arr[] = 7;
  //$arr[11] = 300; // test this

  var_dump($arr);
  /*
  array(5) {
    [0]=>int(1)
    [10]=>int(2)
    [11]=>int(3)
    ["xx"]=>int(4)
    [12]=>int(5)
    [3]=>int(6)
    [13]=>int(7)
  }
  */

  // --------------------------------------------------------

  $arr[true] = true;
  $arr[false] = false;
  $arr[NULL] = NULL;

  var_dump($arr);
  /*
  array(3) {
    [1]=>bool(true)
    [0]=>bool(false)
    [""]=>NULL
  }
  */

  // --------------------------------------------------------

  $arr = [
    ['name' => 'peter', 'age' => 27],
    ['name' => 'kang', 'age' => 28],
    ['name' => 'alex', 'age' => 29],
  ];

  echo '-- 1 --', PHP_EOL;

  var_dump($arr);
  // print_r($arr);

  echo '-- 2 --', PHP_EOL;

  var_dump($arr[0]['name']); // string(5) "peter"

  echo '-- 3 --', PHP_EOL;

  foreach ($arr as $value) {
    var_dump($value);
  }

  echo '-- 4 --', PHP_EOL;

  foreach ($arr as $key => $value) {
    var_dump($key, $value);
  }

_h function.php

<?php
  
  function func() {
    echo '100';
  }

  function func($name) { // error: cannot redeclare func()
    echo $name;
  }

  // --------------------------------------------------------

  $a = 5;

  func1($a);
  echo $a, PHP_EOL;

  func2($a);
  echo $a, PHP_EOL;

  function func1($a) {
    $a = 100;
  }

  function func2(&$a) { // IMPORTANT
    $a = 200;
  }

  // --------------------------------------------------------

  $arr = [];
  func1($arr);
  echo '--- test1 ---', PHP_EOL;
  echo var_dump($arr);

  $arr = [];
  func2($arr);
  echo '--- test2 ---', PHP_EOL;
  echo var_dump($arr); 

  function func1($arr) {
    $arr[0] = 100;
    echo '--- func1 ---', PHP_EOL;
    echo var_dump($arr);
  }

  function func2(&$arr) { // IMPORTANT
    $arr[0] = 100;
    echo '--- func2 ---', PHP_EOL;
    echo var_dump($arr);
  }

  // --------------------------------------------------------

  func(1, 2); // error
  func(1, 2, 3);
  func(1, 2, 3, 4); // work

  function func($a, $b, $c) {
    echo $a, $b, $c;
  }

  // --------------------------------------------------------

  func(10, 5); // error: cannot pass parameter 2 by reference
  
  function func($a, &$b) {
    echo $a, $b;
  }

  // --------------------------------------------------------

  echo var_dump(func());
  
  function func() {
    echo __FUNCTION__, PHP_EOL;
  }

  // --------------------------------------------------------

  $a = 100;
  func();
  echo $a, PHP_EOL; // 110

  function func() {
    // echo $a, PHP_EOL; // notice: undefined variable: a

    $t = $GLOBALS['a'];
    echo $t, PHP_EOL; // 100
    $t += 2;
    echo $t, PHP_EOL; // 102

    $r = &$GLOBALS['a']; // IMPORTANT
    echo $r, PHP_EOL; // 100
    $r += 3;
    echo $r, PHP_EOL; // 103

    global $a, $a2;
    echo $a, PHP_EOL; // 103
    echo $a2, PHP_EOL; //
    echo var_dump($a2); // NULL
    $a += 7;
    echo $a, PHP_EOL; // 110
  }

  // --------------------------------------------------------

  $arr = [];
  func();
  echo var_dump($arr); // array(1) { [0] => int(300) }

  function func() {
    // echo var_dump($arr); // notice: undefined variable: arr
    
    $t = $GLOBALS['arr'];
    echo var_dump($t); // array(0) {}
    $t[0] = 100;
    echo var_dump($t); // array(1) { [0] => int(100) }
    
    $r = &$GLOBALS['arr']; // IMPORTANT
    echo var_dump($r); // array(0) {}
    $r[0] = 200;
    echo var_dump($r); // array(1) { [0] => int(200) }

    global $arr;
    echo var_dump($arr); // array(1) { [0] => int(200) }
    $arr[0] = 300;
    echo var_dump($arr); // array(1) { [0] => int(300) }
  }

  // --------------------------------------------------------

  func();
  echo $a, PHP_EOL; // 100
  echo $GLOBALS['a'], PHP_EOL; // 100

  function func() {
    // global $a = 100; // error: syntax error, unexpected '='
    
    global $a;
    $a = 100;
  }

  // --------------------------------------------------------

  func(); // 1
  func(); // 2
  func(); // 3

  function func() {
    static $count = 1;
    echo $count, PHP_EOL;
    $count++;
  }

  // --------------------------------------------------------

  $str = 'func';
  $str(100);

  function func($a, $b = 0) {
    echo __LINE__, ' ', __FUNCTION__, PHP_EOL;
    echo $a + $b;
  }

  // --------------------------------------------------------

  // $func(); // error: uncaught error: function name must be a string

  $func = function() {
    echo 'Hello', PHP_EOL;
  }; // still need ;

  $func();

  echo gettype($func), PHP_EOL; // object
  echo var_dump($func); // object(Closure)#1 (0) {}

  // --------------------------------------------------------

  $a = 100;

  $func = function() use ($a) {
    echo $a, PHP_EOL;
  };

  $func(); // 100

  echo gettype($func), PHP_EOL; // object
  echo var_dump($func); // object(Closure)#1 (1) {
                        //    ["static"] =>
                        //        array(1) { ["a"] => int(100) }
                        // }

  // --------------------------------------------------------

  func();

  function func() {
    $a = 100;
    
    // $innerFunc1 = function() {
    //   echo $a; // notice: undefined variable: a
    // };
    // $innerFunc1();

    $innerFunc2 = function() use ($a) {
      echo $a; // work
    };
    $innerFunc2();
  }

  // --------------------------------------------------------

  $inner = func();
  $inner(); // 100
  $inner(); // 101
  $inner(); // 102

  echo '--- vs. ---', PHP_EOL;
  
  func()(); // 100
  func()(); // 100
  func()(); // 100
    
  function func() {
    $a = 100;

    $innerFunc = function() use (&$a) { // IMPORTANT
      echo $a++, PHP_EOL;
    };

    return $innerFunc;
  }

_i class.php

<?php

  // TODO

=> ref: https://www.bilibili.com/video/BV14x411o7SL