Ruby Operator Precedence
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In the previous chapter of Ruby Essentials we looked at Ruby operators and expressions. An equally important area to understand is operator precedence. This is essentially the order in which the Ruby interpreter evaluates expressions comprising more than one operator.
An Example of Ruby Operator Precedence
When humans evaluate expressions, they usually do so starting at the left of the expression and working towards the right. For example, working from left to right we get a result of 300 from the following expression:
10 + 20 * 10 = 300
This is because we, as humans, add 10 to 20, resulting in 30 and then multiply that by 10 to arrive at 300. Ask Ruby to perform the same calculation and you get a very different answer:
irb(main):003:0> 10 + 20 * 10 => 210
This is a direct result of operator precedence. Ruby has a set of rules that tell it in which order operators should be evaluated in an expression. Clearly, Ruby considers the multiplication operator (*) to be of a higher precedence than the addition (+) operator.
Overriding Operator Precedence
The precedence built into Ruby can be overridden by surrounding the lower priority section of an expression with parentheses. For example:
(10 + 20) * 10 => 300
In the above example, the expression fragment enclosed in parentheses is evaluated before the higher precedence multiplication.
Operator Precedence Table
The following table provides a reference when you need to know the operator precedence used by Ruby. The table lists all operators from highest precedence to lowest.
Method | Operator | Description |
---|---|---|
Yes | [ ] [ ]= |
Element reference, element set |
Yes | ** |
Exponentiation (raise to the power) |
Yes | ! ~ + - |
Not, complement, unary plus and minus (method names for the last two are +@ and -@ ) |
Yes | * / % |
Multiply, divide, and modulo |
Yes | + - |
Addition and subtraction |
Yes | >> << |
Right and left bitwise shift |
Yes | & |
Bitwise `AND' |
Yes | ^ | |
Bitwise exclusive `OR' and regular `OR' |
Yes | <= < > >= |
Comparison operators |
Yes | <=> == === != =~ !~ |
Equality and pattern match operators (!= and !~ may not be defined as methods) |
&& |
Logical `AND' | |
|| |
Logical `AND' | |
.. ... |
Range (inclusive and exclusive) | |
? : |
Ternary if-then-else | |
= %= { /= -= += |= &= >>= <<= *= &&= ||= **= |
Assignment | |
defined? |
Check if specified symbol defined | |
not |
Logical negation | |
or and |
Logical composition | |
if unless while until |
Expression modifiers | |
begin/end |
Block expression |
Operators with a Yes in the method column are actually methods, and as such may be overridden.
Purchase and download the full PDF and ePub editions of this Ruby eBook for only $8.99 |
Previous | Table of Contents | Next |
Ruby Operators | Ruby Math Functions and Methods |