<?php

/*
   +-------------------------------------------------------------+
   | Copyright (c) 2015 Facebook, Inc. (http://www.facebook.com) |
   +-------------------------------------------------------------+
*/

error_reporting(-1);

// a simple example of passing by value and by reference

function f($p1, &$p2)
{
    echo "f In:  \$p1: $p1, \$p2: $p2\n";
    $p1 = 100;      // only the local copy is changed
    $p2 = 200;      // actual argument's value changed
    echo "f Out: \$p1: $p1, \$p2: $p2\n";
}

///*
$a1 = 10;
$a2 = 20;
var_dump($a1);
var_dump($a2);
f($a1, $a2);        // variable $a2 is passed by reference
var_dump($a1);
var_dump($a2);

$a2 = [10,20,30];
var_dump($a2);
f($a1, $a2[1]); // variable $a2[1] is passed by reference
var_dump($a1);
var_dump($a2);

class C
{
    public $member;
}
$o = new C;
$o->member = "Red";
var_dump($o);
f($a1, $o->member);     // variable $o->member is passed by reference
var_dump($o);
//*/

// passing by reference explored further

function g(&$p1)
{
    echo "g In:  \$p1: $p1\n";
    $p1 = 200;      // actual argument's value changed
    echo "g Out: \$p1: $p1\n";
}

///*
$a2 = 0;
// g(TRUE);             // PHP5 32/64, Error: Only variables can be passed by reference
                           // HHVM,       Error: Cannot pass parameter 1 by reference
   g($a2 = TRUE);       // Suspicious "behavior"
                        // PHP5 32, allowed quietly, but does not change the original argument
                        // PHP5 64  allowed with warning "PHP Strict standards:  Only variables
                        //     should be passed by reference", but does not change the original argument
                           // HHVM, allowed quietly, but does not change the original argument
var_dump($a2);
   $a2 = TRUE;
   g($a2);              // OK; passing a modifiable lvalue by reference
   var_dump($a2);

// following tests have different values for $a2, and give results like the case above

// g(-123);
   g($a2 = -123);
var_dump($a2);
   $a2 = -123;
   g($a2);
var_dump($a2);
// g(1.23e3);
   g($a2 = 1.23e3);
var_dump($a2);
   $a2 = 1.23e3;
   g($a2);
var_dump($a2);
// g(NULL);
   g($a2 = NULL);
var_dump($a2);
   $a2 = NULL;
   g($a2);
var_dump($a2);
// g("abc");
   g($a2 = "abc");
var_dump($a2);
   $a2 = "abc";
   g($a2);
var_dump($a2);
// g([1,2,3]);
   g($a2 = [1,2,3]);
var_dump($a2);
   $a2 = [1,2,3];
   g($a2);
var_dump($a2);
//*/

///*
// based on finding from above, further testing
$z = 10;
// ($z = 5) = 20;      // All 3, Error: unexpected '='
// ($z = 5)++;       // All 3, Error: unexpected '++'
// ($z += 5) = 20;  // All 3, Error: unexpected '='
// ($z += 5)++;     // All 3, Error: unexpected '++'
//*/

///*
$z = 10;
g($z);              // create a reference to a modifiable lvalue
var_dump($z);
// g($z + 1);       // PHP5 32/64, Error: Only variables can be passed by reference
                  // HHVM,       Error: Cannot pass parameter 1 by reference
g($z -= 2);         // PHP5 32, allowed quietly, but does not change the original argument
                    // PHP5 64  allowed with warning "PHP Strict standards:  Only variables
                    //     should be passed by reference", but does not change the original argument
                  // HHVM, allowed quietly, but does not change the original argument
var_dump($z);
g($z = $z - 2);   // same as above
var_dump($z);
// g($z++);         // PHP5 32/64, Error: Only variables can be passed by reference
                  // HHVM,       Error: Cannot pass parameter 1 by reference
// ($z++)++;        // All 3, Error: unexpected '++'
g(--$z);          // PHP5 32, allowed quietly, but does not change the original argument
                    // PHP5 64  allowed with warning "PHP Strict standards:  Only variables
                    //     should be passed by reference", but does not change the original argument
                  // HHVM, allowed quietly, but does not change the original argument
// ----$z;          // All 3, Error: unexpected '--'
var_dump($z);
//*/

///*
function k() { return 10; }
var_dump(k());
g(k());        // PHP5 32, allowed quietly, but (presumably) does not change the original argument
                    // PHP5 64  allowed with warning "PHP Strict standards:  Only variables
                    //     should be passed by reference", but (presumably) does not change the original argument
// k() = 10;   // All 3, Error: Can't use function return value in write context
                    // HHVM, allowed quietly, but (presumably) does not change the original argument
//*/