Editing Assignment (computer science) (section)

===Chained assignment===
A statement like <code>w = x = y = z</code> is called a '''chained assignment''' in which the value of <code>z</code> is assigned to multiple variables <code>w, x,</code> and <code>y</code>. Chained assignments are often used to initialize multiple variables, as in

<code>a = b = c = d = f = 0</code>

Not all programming languages support chained assignment. Chained assignments are equivalent to a sequence of assignments, but the evaluation strategy differs between languages. For simple chained assignments, like initializing multiple variables, the evaluation strategy does not matter, but if the targets (l-values) in the assignment are connected in some way, the evaluation strategy affects the result.

In some programming languages ([[C (programming language)|C]] for example), chained assignments are supported because assignments are expressions, and have values. In this case chain assignment can be implemented by having a [[Operator associativity#Right-associativity of assignment operators|right-associative assignment]], and assignments happen right-to-left. For example, <code>i = arr[i] = f()</code> is equivalent to <code>arr[i] = f(); i = arr[i]</code>. In [[C++]] they are also available for values of class types by declaring the appropriate return type for the assignment operator.

In [[Python (programming language)|Python]], assignment statements are not expressions and thus do not have a value. Instead, chained assignments are a series of statements with multiple targets for a single expression. The assignments are executed left-to-right so that <code>i = arr[i] = f()</code> evaluates the expression <code>f()</code>, then assigns the result to the leftmost target, <code>i</code>, and then assigns the same result to the next target, <code>arr[i]</code>, using the new value of <code>i</code>.<ref>{{cite web|url=https://docs.python.org/reference/simple_stmts.html#assignment-statements|title=7. Simple statements — Python 3.6.5 documentation|website=docs.python.org|access-date=20 April 2018}}</ref> This is essentially equivalent to <code>tmp = f(); i = tmp; arr[i] = tmp</code> though no actual variable is produced for the temporary value.