Immutable vs struct and type vs mutable struct in julia

When working with Julia, you may come across the need to define custom data types. Two common options for defining custom data types in Julia are using immutable structs and mutable structs. Additionally, you may also need to choose between using the type keyword or the struct keyword. In this article, we will explore the differences between these options and provide solutions for each case.

Using Immutable Structs

Immutable structs in Julia are defined using the struct keyword. These structs are similar to tuples, as they cannot be modified once created. This can be useful when you want to ensure that the values of your data type remain constant throughout your program.

struct Person
    name::String
    age::Int
end

In the above example, we define an immutable struct called Person with two fields: name and age. Once a Person object is created, its fields cannot be modified.

Using Mutable Structs

Mutable structs, on the other hand, can be modified after creation. These structs are defined using the mutable struct keyword. This can be useful when you need to update the values of your data type throughout your program.

mutable struct Point
    x::Float64
    y::Float64
end

In the above example, we define a mutable struct called Point with two fields: x and y. The values of these fields can be modified after a Point object is created.

Using Type

The type keyword in Julia is used to define abstract types. These types cannot be instantiated directly, but can be used as a parent type for other types. This can be useful when you want to define a common interface for a group of related types.

abstract type Animal end

struct Dog <: Animal
    name::String
    age::Int
end

struct Cat <: Animal
    name::String
    age::Int
end

In the above example, we define an abstract type called Animal and two subtypes: Dog and Cat. Both Dog and Cat have the same fields: name and age. By using the type keyword, we can define a common interface for all animals.

Conclusion

When choosing between immutable and mutable structs, consider whether you need the ability to modify the values of your data type after creation. If you do not need this ability, immutable structs can provide better performance and safety guarantees. On the other hand, if you need to update the values of your data type, mutable structs are the way to go.

When choosing between using the struct keyword or the type keyword, consider whether you need to define a common interface for a group of related types. If you do, the type keyword can be useful. Otherwise, the struct keyword is sufficient for defining custom data types.

In conclusion, the best option depends on your specific requirements. Consider the trade-offs between immutability and mutability, as well as the need for a common interface, to make an informed decision.