How to make a new type in julia

Julia is a powerful programming language that allows users to create their own custom types. In this article, we will explore three different ways to make a new type in Julia and discuss the pros and cons of each approach.

Option 1: Using the `struct` keyword

One way to create a new type in Julia is by using the `struct` keyword. This approach allows you to define a type with specific fields and their corresponding types. Here’s an example:

struct Person
    name::String
    age::Int
end

In this example, we define a `Person` type with two fields: `name` of type `String` and `age` of type `Int`. To create a new instance of this type, we can simply call the constructor:

person = Person("John Doe", 30)

Option 2: Using the `mutable struct` keyword

If you need to modify the fields of your type after it has been created, you can use the `mutable struct` keyword. This approach allows you to change the values of the fields directly. Here’s an example:

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

In this example, we define a `Point` type with two fields: `x` and `y`, both of type `Float64`. We can modify the values of these fields directly:

point = Point(1.0, 2.0)
point.x = 3.0
point.y = 4.0

Option 3: Using the `abstract type` keyword

If you want to create a type hierarchy, you can use the `abstract type` keyword. This approach allows you to define an abstract type that serves as a base for other types. Here’s an example:

abstract type Animal end

struct Dog <: Animal
    name::String
end

struct Cat <: Animal
    name::String
end

In this example, we define an abstract type `Animal` and two subtypes `Dog` and `Cat`. Both subtypes have a `name` field of type `String`. We can create instances of these subtypes:

dog = Dog("Buddy")
cat = Cat("Whiskers")

Now that we have explored three different ways to make a new type in Julia, let's discuss which option is better.

Option 1, using the `struct` keyword, is the simplest and most straightforward way to create a new type in Julia. It allows you to define the fields and their types explicitly. However, it does not allow for field modification after the type has been created.

Option 2, using the `mutable struct` keyword, is useful when you need to modify the fields of your type after it has been created. However, it introduces mutability, which can make the code harder to reason about and debug.

Option 3, using the `abstract type` keyword, is suitable when you want to create a type hierarchy. It allows you to define a base type and derive subtypes from it. However, it adds complexity to the code and may not be necessary for simpler use cases.

In conclusion, the best option depends on your specific requirements. If you need a simple type with fixed fields, option 1 is the way to go. If you need to modify the fields after creation, option 2 is a good choice. If you want to create a type hierarchy, option 3 provides the necessary flexibility.