Reference assignment operator in PHP, =&

Viewed 80 times

What does the =& (equals-ampersand) assignment operator do in PHP?

Is it deprecated?

Answers

It's not deprecated and is unlikely to be. It's the standard way to, for example, make part of one array or object mirror changes made to another, instead of copying the existing data.

It's called assignment by reference, which, to quote the manual, "means that both variables end up pointing at the same data, and nothing is copied anywhere".

The only thing that is deprecated with =& is "assigning the result of new by reference" in PHP 5, which might be the source of any confusion. new is automatically assigned by reference, so & is redundant/deprecated in$o = &new C;, but not in $o = &$c;.

Since it's hard to search, note that =& (equals ampersand) is the same as = & (equals space ampersand) and is often written such that it runs into the other variable like $x = &$y['z']; or $x = &$someVar (ampersand dollar sign variable name). Example simplified from the docs:

$a = 3;
$b = &$a;
$a = 4;
print "$b"; // prints 4

Here's a handy link to a detailed section on Assign By Reference in the PHP manual. That page is part of a series on references - it's worth taking a minute to read the whole series.

Sunday, November 6, 2022

dannyhobby-6265ff06d3f4

You can see examples about this behaviour in Logical Operators

Also you can read artical about Short-circuit evaluation

The short-circuit expression x Sand y (using Sand to denote the short-circuit variety) is equivalent to the conditional expression if x then y else false; the expression x Sor y is equivalent to if x then true else y.

In php.

return x() and y();

equal to

if (x())
  return (bool)y();
else
  return false;

return x() or y();

equal to

if (x())
  return true;
else
  return (bool)y();

So, deal is not just in precedence.

Saturday, December 3, 2022

alan_plum

Not returning a reference is a waste of resources and a yields a weird design. Why do you want to do a copy for all users of your operator even if almost all of them will discard that value?

a = b; // huh, why does this create an unnecessary copy?

In addition, it would be surprising to users of your class, since the built-in assignment operator doesn't copy likewise

int &a = (some_int = 0); // works

Sunday, October 2, 2022

chevy1006

The short answer is - it isn't defined to work with strings.

Longer answer: if you try the subtraction operator on two strings, it will first cast them to numbers and then perform the arithmetic.

"10" - "2" = 8

If you try something that is non-numeric, you get a NaN related error:

"AA" - "A" = NaN

Tuesday, November 22, 2022

teudimundo

The parameter of an overloaded assignment operator can be any type and it can be passed by reference or by value (well, if the type is not copy constructible, then it can't be passed by value, obviously).

So, for example, you could have an assignment operator that takes an int as a parameter:

MyClass& operator=(int);

The copy assignment operator is a special case of an assignment operator. It is any assignment operator that takes the same type as the class, either by value or by reference (the reference may be const- or volatile-qualified).

If you do not explicitly implement some form of the copy assignment operator, then one is implicitly declared and implemented by the compiler.

Thursday, November 3, 2022

tom_daurizio

Only authorized users can answer the search term. Please sign in first, or register a free account.

Not the answer you're looking for? Browse other questions tagged :

php

operators

assignment-operator

Reference assignment operator in PHP, =&

Answers

php,operators,assignment-operator