Julia Cheat Sheet

Essential Julia syntax for scientific computing, including arrays, broadcasting, multiple dispatch, and the type system.

2 PagesIntermediateMar 22, 2026

Basics

Variables, strings, and functions.

julia

# Variables and printingx = 42name = "Julia"println("Value: ", x)s = "Hello, $name!"   # string interpolationfunction greet(n)    return "Hi, $n"endsquare(x) = x^2          # one-line function

Multiple Dispatch

Methods selected by the types of all arguments.

julia

area(r::Float64) = pi * r^2                  # circlearea(w::Float64, h::Float64) = w * h          # rectanglefunction describe(x::Int)    println("$x is an integer")endfunction describe(x::AbstractString)    println("$x is a string")end

Arrays

Working with Julia's 1-indexed arrays.

zeros(3)- Creates a 3-element array of zeros
arr[1]- Arrays are 1-indexed, not 0-indexed
push!(arr, x)- Appends x; trailing ! marks a mutating function
map(f, arr)- Applies function f to every element
arr .+ 1- Broadcasting: applies + elementwise via dot syntax
size(arr)- Returns a tuple of the array's dimensions

Type System

Defining and inspecting types.

Int64 / Float64- Built-in concrete numeric types
abstract type- Declares a node in the type hierarchy, cannot be instantiated
struct- struct Point x::Float64 y::Float64 end defines an immutable type
mutable struct- Same as struct but fields can be reassigned
typeof(x)- Returns the runtime type of a value
Union{Int, Nothing}- A type that is either Int or Nothing

Pro Tip

Type-annotate hot-path function arguments (e.g. x::Float64) so Julia can specialize and compile fast machine code instead of falling back to slower generic dispatch.

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