php - some questions about the usage of Iterator function -


code from:http://php.net/manual/en/class.iterator.php(example #1 basic usage)

<?php class myiterator implements iterator {     private $position = 0;     private $array = array(         "firstelement",         "secondelement",         "lastelement",     );        public function __construct() {         $this->position = 0;     }      function rewind() {         var_dump(__method__);         $this->position = 0;     }      function current() {         var_dump(__method__);         return $this->array[$this->position];     }      function key() {         var_dump(__method__);         return $this->position;     }      function next() {         var_dump(__method__);         ++$this->position;     }      function valid() {         var_dump(__method__);         return isset($this->array[$this->position]);     } }  $it = new myiterator;  foreach($it $key => $value) {     var_dump($key, $value);     echo "\n"; } ?>

output is:

string 'myiterator::rewind' (length=18)  string 'myiterator::valid' (length=17)  string 'myiterator::current' (length=19)  string 'myiterator::key' (length=15)  int 0  string 'firstelement' (length=12)  string 'myiterator::next' (length=16)  string 'myiterator::valid' (length=17)  string 'myiterator::current' (length=19)  string 'myiterator::key' (length=15)  int 1  string 'secondelement' (length=13)  string 'myiterator::next' (length=16)  string 'myiterator::valid' (length=17)  string 'myiterator::current' (length=19)  string 'myiterator::key' (length=15)  int 2  string 'lastelement' (length=11)  string 'myiterator::next' (length=16)  string 'myiterator::valid' (length=17)

so can see: 1st, order of function(var_dump(__method__)) output is:

string 'myiterator::rewind' (length=18) string 'myiterator::valid' (length=17) string 'myiterator::current' (length=19) string 'myiterator::key' (length=15)

2nd , 3rd, order of function output is: order of function output is:

string 'myiterator::next' (length=16) string 'myiterator::valid' (length=17) string 'myiterator::current' (length=19) string 'myiterator::key' (length=15)

4rd, order of function output is:

string 'myiterator::next' (length=16) string 'myiterator::valid' (length=17)

my question is:

  1. there 5 functions: rewind();current(); key(); next(); valid(); why functions seems not execute sometimes? eg, can not see myiterator::next in 1st function output. , rewind() shows 1 time.
  2. there 3 values in $array, supposed foreach run 3 times, can see string 'myiterator::valid' (length=17) appear 4 times, why?

the first part initialization of for-loop. calls rewind move cursor beginning of list. that's why don't see next there.

the last part next then, for-loop realizes end of list reached, because valid returned false. valid called 4 times, 3 times returning true, returning false once. how for-loop know stop otherwise?


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