Julia as a Second Language

7 Understanding types

This chapter covers

• Understanding type hierarchies
• Differences between abstract and concrete types
• Combining primitive types to make composite types
• Harnessing the power of multiple dispatch to solve complex tasks elegantly
• How multiple dispatch differs from single dispatch in object-oriented languages¹

All objects in Julia are of a particular type. Remember, you can use typeof to discover the type of any object:

julia> typeof(42)
Int64
 
julia> typeof('A')
Char
julia> typeof("hello")
String

The type decides what you can do with an object. For example, a dictionary allows you to look up a value by key, while an array stores elements in order. An expression evaluating to a Bool value, such as true or false, can be used in ...