assignment.md

title	Assignment
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Assignment

In Ruby, assignment uses the = (equals sign) character. This example assigns the number five to the local variable v:

v=5

Assignment creates a local variable if the variable was not previously referenced.

Abbreviated Assignment

You can mix several of the operators and assignment. To add 1 to an object you can write:

a=1a += 2pa# prints 3

This is equivalent to:

a=1a=a + 2pa# prints 3

You can use the following operators this way: +, -, *, /, %, **, &, |, ^, <<, >>

There are also ||= and &&=. The former makes an assignment if the value was nil or false while the latter makes an assignment if the value was not nil or false.

Here is an example:

a ||= 0a &&= 1pa# prints 1

Note that these two operators behave more like a || a = 0 than a = a || 0.

Multiple Assignment

You can assign multiple values on the right-hand side to multiple variables:

a,b=1,2pa: a,b: b# prints {:a=>1, :b=>2}

In the following sections any place "variable" is used an assignment method, instance, class or global will also work:

defvalue=(value)passigned: valueendself.value, $global =1,2# prints {:assigned=>1}p $global # prints 2

You can use multiple assignment to swap two values in-place:

old_value=1new_value,old_value=old_value,2pnew_value: new_value,old_value: old_value# prints {:new_value=>1, :old_value=>2}

If you have more values on the right hand side of the assignment than variables on the left hand side, the extra values are ignored:

a,b=1,2,3pa: a,b: b# prints {:a=>1, :b=>2}

You can use * to gather extra values on the right-hand side of the assignment.

a, *b=1,2,3pa: a,b: b# prints {:a=>1, :b=>[2, 3]}

The * can appear anywhere on the left-hand side:

*a,b=1,2,3pa: a,b: b# prints {:a=>[1, 2], :b=>3}

But you may only use one * in an assignment.

Array Decomposition

Like Array decomposition in method arguments you can decompose an Array during assignment using parenthesis:

(a,b)=[1,2]pa: a,b: b# prints {:a=>1, :b=>2}

You can decompose an Array as part of a larger multiple assignment:

a,(b,c)=1,[2,3]pa: a,b: b,c: c# prints {:a=>1, :b=>2, :c=>3}

Since each decomposition is considered its own multiple assignment you can use * to gather arguments in the decomposition:

a,(b, *c), *d=1,[2,3,4],5,6pa: a,b: b,c: c,d: d# prints {:a=>1, :b=>2, :c=>[3, 4], :d=>[5, 6]}