julia/QuantumLab Cheat Sheet

Getting started
Group Keyword Explanation
Data Types abstract only for internal nodes of the type-tree
Data Types bitstype N basal type of length N bits
Data Types type like a struct in C
Data Types immutable type that is totally defined by the values of its fields
Other Types TupleTypes e.g. (a,b,c), covariant with a,b,c
Other Types UnionTypes (e.g. Union(a,b,c))
Parametric Types type ...{T} invariant with T
Parametric Types abstract ...{T}
Parametric Types Type{T} only T <: Type{T}
Parametric Types bitstype N ...{T} T is only an abstract tag
Typealias typealias e.g. typealias Matrix{T} Array{T,2}
  • Avoid global variables (at least declare them const or annotate their types at the point of use)
  • Always at least @time and pay attention to memory allocations (they might be a sign for type instability)
  • @profile and ProfileView.view()
  • @allocated or julia –track-allocation=user
  • @code_warntype
  • Lint and TypeCheck (if they work)
  • Don’t use abstract types as parameters to parametric types (including Arrays)
  • Don’t use abstract types for fields of a type (rather make the type parametric instead)
  • When you know the explicit type to an abstract type given to your function, declare it on first use (this automatically makes for a runtime type check)
  • sizehint!
  • for i in 1:3 getfield(obj,i) end is faster than for f in fieldnames(obj) obj.(f) end
  • push! is faster than append! when adding a single element
Tips and Tricks
  • symlink /usr/share/julia/base (or equivalent on other OSs) to an easy to access location for quick reference (e.g. ~/juliabase)
  • ~/juliabase/latex_symbols.jl is the reference for latex-codes (unicode input)
  • adam-p has a comprehensive Markdown-Cheatsheet



Module Import vs. Using
if MyModule exports x but a not necessarily:
Import Command Into Scope
using MyModule x; MyModule.a
using MyModule.a a
using MyModule:a a
import MyModule MyModule.a
import MyModule.a a
import MyModule:a a
importall MyModule x
Module Search Path
Command Search Location
using Modulename $PATH/*
using("Modulename") $pwd/Modulename.jl
Control Flow
Expression Type Code
Compound Expressions begin and (;).
Conditional Evaluation if-elseif-else and ?: (ternary operator).
Short-Circuit Evaluation &amp;&amp;, || and chained comparisons.
Repeated Evaluation, Loops while and for.
Exception Handling try-catch, error() and throw().
Tasks (aka Coroutines) yieldto().
Representation Layers

Name obtained by comment
1 AST :f
2 Lowered AST @code_lowered f(x) desugared and unnested
3 Typed AST @code_typed f(x) type-inferred and optimized
4 LLVM @code_llvm f(x)
5 Assembly @code_native f(x) machine-specific