Which of the following is best for memory usage? - php

Question

Which of the following is best for memory usage?
$a = new foo();
$username = $a->getuserName('username');
$b = new bar();
$b->validateUserName($username);
//OR
( new bar() )->validateUserName( (new foo() )->getuserName($username) );
Does storing an object in a variable increase memory usage?
does PHP treats other languages differently?
Someone can explain the management of PHP memory (should and should not)

Answer 1

To test memory usage you can use the next template:
<?php
$mem = 0; // create variable before "memory_get_usage()";
$mem = memory_get_usage();
// Place your code here
$mem = memory_get_usage() - $mem;
print ("Memory used: $mem");
For example I created the stub:
<?php
class foo {
function getuserName($a) {
return $a;
}
}
class bar {
function validateUserName($a) {
}
}
$mem = 0; // Allocate variable before "memory_get_usage()";
$mem = memory_get_usage();
$a = new foo();
$username = $a->getuserName('username');
$b = new bar();
$b->validateUserName($username);
$mem = memory_get_usage() - $mem;
print ("Memory used: $mem\r\n");
result on php 5.6.40 win x64 is 560 bytes.
If I change the code to your second variant
...
$mem = 0; // Allocate variable before "memory_get_usage()";
$mem = memory_get_usage();
// Note I've changed $username to 'username'
(new bar())->validateUserName( (new foo())->getuserName('username') );
$mem = memory_get_usage() - $mem;
print ("Memory used: $mem\r\n");
Now result is 0 bytes.
Let's see another variant:
...
function test() {
$a = new foo();
$username = $a->getuserName('username');
$b = new bar();
$b->validateUserName($username);
}
$mem = 0; // Allocate variable before "memory_get_usage()";
$mem = memory_get_usage();
test();
$mem = memory_get_usage() - $mem;
print ("Memory used: $mem\r\n");
Memory used: 64
Let's change the function to the second variant:
...
function test() {
(new bar())->validateUserName( (new foo())->getuserName('username') );
}
...
Now result again is 64 bytes.
And one more test:
...
$mem = 0; // Allocate variable before "memory_get_usage()";
$mem = memory_get_usage();
$a = new foo();
$username = $a->getuserName('username');
$b = new bar();
$b->validateUserName($username);
unset($a);
unset($b);
unset($username);
$mem = memory_get_usage() - $mem;
print ("Memory used: $mem\r\n");
Here result is 0 again.
From there I can assume, when you're creating global variables, they remains all the time, and object they are referencing cannot be garbage collected, so they remain in the memory. As soon as you unset variables, or declare them in a particular scope (function), or do not declare them at all - there is no difference in result. To see when object are destroyed and memory is freed you can add desctructors in the classes:
...
function __destruct() {
print "foo/bar destroyed\r\n";
}
...
Still, writing calls in one single line does not allocate unnecessary variables at all, thus improving execution time.
But my recommendation: do not bother with such optimizations in a language such as php. The language itself is not that fast and not that memory effective. For example, adding each item into array may cost more than 100 bytes of memory. Sparing several bytes by making code less readable is not worth it.