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0 pointspaulddraper9y ago0 comments

> The common use of the term though is still what Java has.

The way you are defining "reference" makes it immaterially different from "pointer".

Can a pointer be null? Yes, in C.

Can a "reference" be null? Yes, in Java.

Can a pointer be used in arithmetic operations? Yes, in C.

Can a pointer not be used in arithmetic operations? Yes, in Go.

If this is really the common definition, it isn't a useful one.

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3 comments · 1 top-level

coldtea9y ago· 2 in thread

Whether a thing can be null or not is orthogonal to whether it is a pointer or a reference.

The main difference in this definition is on whether you need to dereference to access the value pointed at (like you do in C) or not.

paulddraperOP9y ago

Not sure I understand you. A concrete PHP example:

   function noop($a, $b) {
     $tmp = $a;
     $a = $b;
     $b = $tmp;
   }

   function swap(&$c, &$d) {
      $tmp = $c;
      $c = $d;
      $d = $tmp;
   }

   $first = [1, 2];
   $second = [3, 4];
   noop($first, $second);
   swap($first, $second);

$a and $b work much differently than $c and $d.

I would call the first two pointers (to [1,2] and [3,4]), and the latter two references (to $first and $second). What would you call them?

(Note: the latter function is impossible to write in Java.)

coldtea9y ago

>I would call the first two pointers (to [1,2] and [3,4]), and the latter two references (to $first and $second). What would you call them?

In the first case, $a and $b pass the arrays by copying their values. The second example uses references.

Java can't do the change visible externally because it passes its references by value -- but that's not a necessity for all languages with references.

As the PHP manual itself says: "References in PHP are a means to access the same variable content by different names. They are not like C pointers; for instance, you cannot perform pointer arithmetic using them, they are not actual memory addresses, and so on".

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