Book Image

Julia 1.0 Programming - Second Edition

By : Ivo Balbaert
Book Image

Julia 1.0 Programming - Second Edition

By: Ivo Balbaert

Overview of this book

The release of Julia 1.0 is now ready to change the technical world by combining the high productivity and ease of use of Python and R with the lightning-fast speed of C++. Julia 1.0 programming gives you a head start in tackling your numerical and data problems. You will begin by learning how to set up a running Julia platform, before exploring its various built-in types. With the help of practical examples, this book walks you through two important collection types: arrays and matrices. In addition to this, you will be taken through how type conversions and promotions work. In the course of the book, you will be introduced to the homo-iconicity and metaprogramming concepts in Julia. You will understand how Julia provides different ways to interact with an operating system, as well as other languages, and then you'll discover what macros are. Once you have grasped the basics, you’ll study what makes Julia suitable for numerical and scientific computing, and learn about the features provided by Julia. By the end of this book, you will also have learned how to run external programs. This book covers all you need to know about Julia in order to leverage its high speed and efficiency for your applications.
Table of Contents (17 chapters)
Title Page
Copyright and Credits
Packt Upsell

Type annotations

As we saw in Chapter 2, Variables, Types, and Operations, type-annotating a variable is done with the :: operator, such as in the function definition function write(io::IO, s::String) #... end, where the parameter io has to be of type IO, and s of type String. To put it differently, io has to be an instance of type IO, and s an instance of type String. The :: operator is, in fact, an assertion that affirms that the value on the left is of the type on the right. If this is not true, a typeassert error is thrown. Try this out in the REPL:

# see the code in Chapter 6\conversions.jl: 

We get an ERROR: TypeError: in typeassert, expected Float64, got Int64 error message.

This is, in addition to the method specialization for multiple dispatch, an important reason why type annotations are used in function signatures.

The operator :: can also be used in the sense of a type declaration, but only in local scope, such as in functions, as follows:

n::Int16 or local n::Int16...