Julia Data Types

While Julia is a dynamically typed language, values have a concrete type.

Abstract Types

Abstract types should not be used directly. They are supertypes that categorize behaviors. They are however useful for constructing a novel data type, or for typing the arguments to a function.

The primary set of abstract types, with their hierarchy of supertypes and subtypes indicated by indentation, is:

• Number

  • Real

    • AbstractFloat

    • Integer

      • Signed

      • Unsigned

• AbstractChar

• AbstractString

• AbstractArray

  • AbstractVector

  • AbstractMatrix

  • AbstractRange

Numeric Types

The set of primitive types that descend from the Number abstract type are:

• Bool

• Int8

• Int16

• Int32

• Int64

• Int128

• UInt8

• UInt16

• UInt32

• UInt64

• UInt128

• Float16

• Float32

• Float64

String Types

String is a subtype of AbstractString that implicitly is encoded in UTF-8.

Packages may create novel subtypes of AbstractString, so consider typing string arguments for functions as AbstractString rather than String.

Char is a subtype of AbstractChar, and is a 32-bit representation a Unicode character.

Composite Types

Structs are a composite data type. Struct values can be instantiated like:

julia> struct Foo
           bar
           baz
           qux
       end

julia> foo = Foo("Hello, world.", 23, 1.5)
Foo("Hello, world.", 23, 1.5)

Fields are accessed by the dot operator.

julia> foo.bar
"Hello, world."

By default, struct objects are immutable.

Collection Types

Values can be collected in a variety of series types.

The Array type is a general purpose series of values, all of the same type. Both Vector and Matrix types descend from AbstractArray.

The range operator (:) creates collections that have some type descending from AbstractRange, which also descends from AbstractArray. The differences between e.g. UnitRange and OrdinalRange relate to the available optimizations.

== Nothing Type ===

The singleton constant nothing is of type Nothing.

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