Variables

Julia provides an extremely flexible system for naming variables. Variable names are case-sensitive, and have no semantic meaning (that is, the language will not treat variables differently based on their names).

julia> ix = 1.0
1.0

julia> y = -3
-3

julia> Z = "My string"
"My string"

julia> customary_phrase = "Hello world!"
"Hello world!"

julia> UniversalDeclarationOfHumanRightsStart = "人人生而自由，在尊严和权力上一律平等。"
"人人生而自由，在尊严和权力上一律平等。"

Unicode names (in UTF-8 encoding) are allowed:

julia> δ = 0.00001
0.00001

julia> 안녕하세요 = "Hello"
"Hello"

Julia will even let you redefine built-in constants and functions if needed:

julia> pi
π = 3.1415926535897...

julia> pi = 3
Warning: imported binding for pi overwritten in module Main
3

julia> pi
3

julia> sqrt = 4
4

However, this is obviously not recommended to avoid potential confusion.

Allowed Variable Names

Variable names must begin with a letter (A-Z or a-z), underscore, or Unicode character with code point greater than 00A0. Subsequent characters may also include ! and digits (0-9).

All operators are also valid identifiers, but are parsed specially. In some contexts operators can be used just like variables; for example (+) refers to the addition function, and (+) = f will reassign it.

The only explicitly disallowed names for variables are the names of built-in statements:

julia> else = false
ERROR: syntax: unexpected else

julia> try = "No"
ERROR: syntax: unexpected =

Stylistic Conventions

While Julia imposes few restrictions on valid names, it has become useful to adopt the following conventions:

• Names of variables are in lower case.
• Word separation can be indicated by underscores ('\_'), but use of underscores is discouraged unless the name would be hard to read otherwise.
• Names of Types begin with a capital letter and word separation is shown with CamelCase instead of underscores.
• Names of functions and macros are in lower case, without underscores.
• Functions that modify their inputs have names that end in !. These functions are sometimes called mutating functions or in-place functions.