Parametric types in Julia

The T in braces is chosen per use and bounded by <:.

# The T in curly braces is decided per use; constraints bound it.
struct Reading{T<:Real}
    label::String
    value::T
end

seeing = Reading("seeing", 2.3)
frames = Reading("frames", 48)
println(typeof(seeing))
println(typeof(frames))

# Parametric functions dispatch on the element type.
midpoint(xs::Vector{T}) where {T<:Real} = (first(xs) + last(xs)) / 2
println(midpoint([10.0, 14.0, 22.0]))
println(midpoint([3, 9]))

How it works

1. Reading{T<:Real} stamps a concrete type per value.
2. typeof shows Reading{Float64} and Reading{Int64}.
3. where {T<:Real} writes the same idea on a function.

Keywords and builtins used here

• Reading
• Real
• String
• T
• Vector
• end
• struct
• where

The run, in numbers

Lines

15

Characters to type

415

Tokens

103

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 103 seconds.

Type this snippet

Step 3 of 3 in Types, step 18 of 27 in Language basics.

← Previous Next →