Some interesting Julia codes

Tue, 17 Mar 2026 12:04:42 +0100

Julia is fast, composable, dynamic, general, reproducible and open source. The codes below were taken from https://julialang.org. I found it very illustrating.

Multiple dispatch

struct Dog end
struct Cat end

dog, cat = Dog(), Cat()
meet(a::Dog, b::Dog) = "The dogs play together"
meet(a::Dog, b::Cat) = "The dog chases the cat"
meet(a::Cat, b::Dog) = "The cat hisses at the dog"
meet(a::Cat, b::Cat) = "The cats ignore each other"

meet(dog, cat)
meet(dog, dog)
meet(cat, cat)

Display customization

struct Nutshell{T}
	contents::T
end
Base.show(io::IO, n::Nutshell) = print(io, "🥜 ", n.contents, " 🥜")
Nutshell("Julia")

Unicode and math

α, β = .5, .3
f(x) = α * x + β
Σ(v) = reduce(+, v)
Σ(f.(1:5))

Comprehensions

[x^2 for x in 1:5]

Broadcasting

A = [1 2; 3 4]
sin.(A) .+ 1
Dict(c => i for (i, c) in enumerate("julia")

Piping and composition

1:5 |> sum |> sqrt
(sqrt ∘ sum)(1:5) # equiv. above
map(exp ∘ abs, [-1, 2, -3])

Destructuring

(a, b, c) = 1:3
a, c # => (1, 3)
head, tail... = ["first", "second", "third"]
head, tail # => ("first", ["second", "third"])

Metaprogramming

ex = :(1 + 2 * 3)
typeof(ex) # => Expr
eval(ex)   # => 7

Easy package install

using DataFrames
# if not installed, prompted for installation, after 'y' answer
df = DataFrame(name = ["Alice", "Bob"], age = [25, 30])

Defaults and keywords args

function greet(name, greeting = "Hello"; punctuation = "!")
	"$greeting, $name$puctuation"
end
greet("Julia")  # "Hello, Julia!"
greet("world", "Hi"; puctuation = ".") # "Hi, world."

Multi-threading

function fib(n)
	n < 2 && return n
	t = Threads.@spawn fib(n-2)
	return fib(n-1) + fetch(t)
end
fib(10)
Threads.nthreads() # => threads assigned to Julia

Build-in REPL modes

# Default Julia mode, backspace from other modes
# Press ] for package mode
# Press ; for shell mode
# Press ? for helps
# Press $ for R mode, if RCall.jl is installed

Code introspection (simplified)

f(x, y) = x + y
@code_warntype f(1, 2)
@code_llvm f(1, 2)
@code_native f(1, 2)

Julia on Breeding and genetics

Some interesting Julia codes

Multiple dispatch

Display customization

Unicode and math

Comprehensions

Broadcasting

Piping and composition

Destructuring

Metaprogramming

Easy package install

Defaults and keywords args

Multi-threading

Build-in REPL modes

Code introspection (simplified)