Parametric methods revisited

The ability to dispatch to various methods based upon subtyping relationships is a key feature of the Julia language. We initially introduced the concept of parametric methods in Chapter 3, Designing Functions and Interfaces. In this section, we will go a little deeper and examine some subtle situations about how methods are selected for dispatch.

Let's start with the basics: how do we specify type variables for parametric methods?

Specifying type variables

When we define a parametric method, we use the where clause to introduce type variables. Let's go over a simple example:

triple(x::Array{T,1}) where {T <: Real} = 3x

The triple function takes an Array{T}, where T is any subtype...