How to use dot notation when extending functions for a user defined type

When working with Julia, it is common to extend functions for user-defined types. This allows you to define behavior specific to your custom types. However, when extending functions, you may encounter situations where you want to use dot notation to apply the function element-wise to arrays of your custom type. In this article, we will explore three different ways to achieve this.

Option 1: Using a for loop

One way to use dot notation when extending functions for a user-defined type is by using a for loop. This approach involves iterating over the elements of the array and applying the function to each element individually. Here’s an example:


struct MyType
    value::Float64
end

function myfunction(x::MyType)
    return x.value + 1
end

function myfunction(arr::Array{MyType, 1})
    result = similar(arr)
    for i in eachindex(arr)
        result[i] = myfunction(arr[i])
    end
    return result
end

arr = [MyType(1.0), MyType(2.0), MyType(3.0)]
result = myfunction(arr)

This approach works well and allows you to use dot notation when applying the function to arrays of your custom type. However, it can be a bit cumbersome and may not be the most efficient solution.

Option 2: Using broadcasting

An alternative approach is to use broadcasting. Broadcasting allows you to apply a function element-wise to arrays without the need for a for loop. Here’s how you can use broadcasting to extend functions for a user-defined type:


struct MyType
    value::Float64
end

function myfunction(x::MyType)
    return x.value + 1
end

Base.broadcasted(f::Function, x::MyType) = myfunction(x)

arr = [MyType(1.0), MyType(2.0), MyType(3.0)]
result = myfunction.(arr)

This approach is more concise and allows you to use dot notation directly when applying the function to arrays of your custom type. Broadcasting takes care of applying the function element-wise without the need for a for loop.

Option 3: Using the dot operator

Julia also provides the dot operator, which allows you to use dot notation when extending functions for a user-defined type. Here’s how you can use the dot operator:


struct MyType
    value::Float64
end

function myfunction(x::MyType)
    return x.value + 1
end

Base.:.(f::Function, x::MyType) = myfunction(x)

arr = [MyType(1.0), MyType(2.0), MyType(3.0)]
result = myfunction.(arr)

This approach is similar to using broadcasting but allows you to define the behavior directly in the function definition. The dot operator is a powerful tool for extending functions and provides a concise way to use dot notation.

After exploring these three options, the best approach depends on your specific use case. If performance is a concern, using broadcasting or the dot operator may be more efficient than using a for loop. However, if simplicity and readability are more important, using a for loop may be a better choice. Ultimately, it is up to you to decide which option suits your needs best.

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