为什么代码表现为这种方式WRT引用返回？

Question

This is my setting:
display_startup_errors = on
display_errors = On
error_reporting = E_ALL | E_STRICT

$b;
function func ($name) {
  global $b;
  $b = 10;
  return $b;
  }
$a =& func("myname");
++$a ;
echo '<br/>$a= '.$a.' $b= ' .$b."<br/>";
xdebug_debug_zval('a'); echo "<br/> ";

The above code output's the following notice:

Strict standards: Only variables should be assigned by reference in /path/to/file/file.php on line 'some line number'
$a= 11 $b= 10
a: (refcount=1, is_ref=0)=11

Why is the above code displaying the notice? And why is there a C.O.W (copy on write) taking place?

$b;
function &func ($name) {//change here: to return a reference.
  global $b;
  $b = 10;
  return $b;
  }
$a =& func("myname");
++$a ;
echo '<br/>$a= '.$a.' $b= ' .$b."<br/>";
xdebug_debug_zval('a'); echo "<br/> ";

The above code will output:

$a= 11 $b= 11
a: (refcount=1, is_ref=1)=11

Why is no strict standards notice thrown here? And here the reference works.

$b;
function &func ($name) {
  global $b;
  $b = 10;
  return $b;
  }
$a = func("myname"); //change here: removed &
++$a ;
echo '<br/>$a= '.$a.' $b= ' .$b."<br/>";
xdebug_debug_zval('a'); echo "<br/> ";

The above code will output:

$a= 11 $b= 10
a: (refcount=1, is_ref=0)=11

Why does a C.O.W take place here?

For info on xdebug_debug_zval visit here.

Answer 1

How the hell did I miss this: This completely mutes my question! from Returning References at PHP manual

Note: If you try to return a reference from a function with the syntax: return ($this->value); this will not work as you are attempting to return the result of an expression, and not a variable, by reference. You can only return variables by reference from a function - nothing else. Since PHP 4.4.0 in the PHP 4 branch, and PHP 5.1.0 in the PHP 5 branch, an E_NOTICE error is issued if the code tries to return a dynamic expression or a result of the new operator.

To use the returned reference, you must use reference assigment:

<?php
function &collector() {
  static $collection = array();
  return $collection;
}
$collection = &collector();
$collection[] = 'foo';
?>