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    <p>The advantage of initializing properties outside of the constructor is that someone reading your code will immediatly know its a default value.</p> <p>Inconvenient is you cannot use every kind of data this way -- will not work with object instanciations, for instance, or with heredoc syntax, from what I recall.</p> <p><br> I don't think there is much of a difference when it comes to performance -- anyway, there are probably lots of things that matter a lot more, in your application ;-)</p> <p><br> Still, purely for fun, using the Vulcan Logic Disassembler :</p> <p>With the first example of code (<code>temp-2.php</code>) :</p> <pre><code>&lt;?php class TestClass { private $test_var = 'Default Value'; function __construct() { } } $a = new TestClass(); </code></pre> <p>You get these opcodes :</p> <pre><code>$ php -d extension=vld.so -d vld.active=1 temp-2.php Branch analysis from position: 0 Return found filename: /home/squale/developpement/tests/temp/temp-2.php function name: (null) number of ops: 11 compiled vars: !0 = $a line # op fetch ext return operands ------------------------------------------------------------------------------- 2 0 EXT_STMT 1 NOP 7 2 EXT_STMT 3 ZEND_FETCH_CLASS :1 'TestClass' 4 EXT_FCALL_BEGIN 5 NEW $2 :1 6 DO_FCALL_BY_NAME 0 7 EXT_FCALL_END 8 ASSIGN !0, $2 9 RETURN 1 10* ZEND_HANDLE_EXCEPTION Class TestClass: Function __construct: Branch analysis from position: 0 Return found filename: /home/squale/developpement/tests/temp/temp-2.php function name: __construct number of ops: 4 compiled vars: none line # op fetch ext return operands ------------------------------------------------------------------------------- 4 0 EXT_NOP 5 1 EXT_STMT 2 RETURN null 3* ZEND_HANDLE_EXCEPTION End of function __construct. End of class TestClass. </code></pre> <p>While, with the second example of code (<code>temp-3.php</code>) :</p> <pre><code>&lt;?php class TestClass2 { private $test_var; function __construct() { $this-&gt;test_var = 'Default Value'; } } $a = new TestClass2(); </code></pre> <p>You get those opcodes :</p> <pre><code>$ php -d extension=vld.so -d vld.active=1 temp-3.php Branch analysis from position: 0 Return found filename: /home/squale/developpement/tests/temp/temp-3.php function name: (null) number of ops: 11 compiled vars: !0 = $a line # op fetch ext return operands ------------------------------------------------------------------------------- 2 0 EXT_STMT 1 NOP 8 2 EXT_STMT 3 ZEND_FETCH_CLASS :1 'TestClass2' 4 EXT_FCALL_BEGIN 5 NEW $2 :1 6 DO_FCALL_BY_NAME 0 7 EXT_FCALL_END 8 ASSIGN !0, $2 9 9 RETURN 1 10* ZEND_HANDLE_EXCEPTION Class TestClass2: Function __construct: Branch analysis from position: 0 Return found filename: /home/squale/developpement/tests/temp/temp-3.php function name: __construct number of ops: 7 compiled vars: none line # op fetch ext return operands ------------------------------------------------------------------------------- 4 0 EXT_NOP 5 1 EXT_STMT 2 ZEND_ASSIGN_OBJ 'test_var' 3 ZEND_OP_DATA 'Default+Value' 6 4 EXT_STMT 5 RETURN null 6* ZEND_HANDLE_EXCEPTION End of function __construct. End of class TestClass2. </code></pre> <p>So, I'm guessing there is a bit of a difference... But not that important ^^</p> <p>Up to you to interpret the opcodes -- but the funny thing is there is no trace of '<code>Default Value</code>' in the first dump... interesting, actually ^^ <br>Seems VLD cannot (or just doesn't) dump everything :-(</p>
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    1. CO+1 for php disassemble
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    2. COExcelent answer :) Thank you
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    3. COYou're welcome :-) Have fun!
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