Go in Action

Erik St. Martin, William Kennedy, Brian Ketelsen

• Publisher: Manning
• Year: 2015
• ISBN:
  9781638352020
• Topic: Computer Science
• Subtopic: Programming
• Index: Computer Science

Summary Go in Action introduces the Go language, guiding you from inquisitive developer to Go guru. The book begins by introducing the unique features and concepts of Go. Then, you'll get hands-on experience writing real-world applications including websites and network servers, as well as techniques to manipulate and convert data at speeds that will make your friends jealous.Purchase of the print book includes a free eBook in PDF, Kindle, and ePub formats from Manning Publications. About the Technology Application development can be tricky enough even when you aren't dealing with complex systems programming problems like web-scale concurrency and real-time performance. While it's possible to solve these common issues with additional tools and frameworks, Go handles them right out of the box, making for a more natural and productive coding experience. Developed at Google, Go powers nimble startups as well as big enterprises—companies that rely on high-performing services in their infrastructure. About the Book Go in Action is for any intermediate-level developer who has experience with other programming languages and wants a jump-start in learning Go or a more thorough understanding of the language and its internals. This book provides an intensive, comprehensive, and idiomatic view of Go. It focuses on the specification and implementation of the language, including topics like language syntax, Go's type system, concurrency, channels, and testing. What's Inside

• Language specification and implementation
• Go's type system
• Internals of Go's data structures
• Testing and benchmarking

About the Reader This book assumes you're a working developer proficient with another language like Java, Ruby, Python, C#, or C++. About the Authors William Kennedy is a seasoned software developer and author of the blog GoingGo.Net. Brian Ketelsen and Erik St. Martin are the organizers of GopherCon and coauthors of the Go-based Skynet framework. Table of Contents

• Introducing Go
• Go quick-start
• Packaging and tooling
• Arrays, slices, and maps
• Go's type system
• Concurrency
• Concurrency patterns
• Standard library
• Testing and benchmarking

Chapter 1. Introducing Go

In this chapter

• Solving modern computing challenges with Go
• Using the Go tools

Computers have evolved, but programming languages haven’t kept up the same pace of evolution. The cell phones we carry might have more CPU cores than the first computer we used. High-powered servers now have 64, 128, or even more cores, but we’re still programming using the techniques we were using for a single core.

The art of programming has evolved too. Most programs aren’t written by a single developer any more: they’re written by teams of people sitting in different time zones and working at different times of the day. Large projects are broken up into smaller pieces and assigned to programmers who then deliver their work back to the team in the form of a library or package that can be used across an entire suite of applications.

Today’s programmers and companies believe more than ever in the power of open source software. Go is a programming language that makes sharing code easy. Go ships with tools that make it simple to use packages written by others, and Go makes it easy to share our own packages too.

In this chapter you’ll see how Go is different from other programming languages. Go rethinks the traditional object-oriented development you might be used to, while still providing an efficient means for code reuse. Go makes it easier for you to effectively use all of the cores on your expensive server, and it takes away the penalty of compiling a very large project.

As you read this chapter, you’ll get a feeling for the many decisions that shaped the creation of Go, from its concurrency model to its lightning-fast compiler. We mentioned it in the preface, but it bears repeating: this book has been written for an intermediate-level developer who has some experience with other programming languages and wants to learn Go. Our goal in writing this book is to provide you an intensive, comprehensive, and idiomatic view of the language. We focus on both the specification and implementation of the language, including the wide-ranging topics of language syntax, Go’s type system, concurrency, channels, testing, and more. We believe this book is perfect for anyone who wants a jump-start in learning Go or who wants a more thorough understanding of the language and its internals.

The source code for the examples in the book is available at https://github.com/goinaction/code.

We hope you’ll appreciate the tools that ship with Go to make your life as a developer easier. In the end, you’ll appreciate why so many developers are choosing Go when they start up that new project.

1.1. Solving modern programming challenges with Go

The Go team went to great lengths to solve the problems facing software developers today. Developers have to make an uncomfortable choice between rapid development and performance when choosing a language for their projects. Languages like C and C++ offer fast execution, whereas languages like Ruby and Python offer rapid development. Go bridges these competing worlds and offers a high-performance language with features that make development fast.

As we explore Go, you’ll find well-planned features and concise syntax. As a language, Go is defined not only by what it includes, but by what it doesn’t include. Go has a concise syntax with few keywords to memorize. Go has a compiler that’s so fast, sometimes you’ll forget it’s running. As a Go developer, you’ll spend significantly less time waiting for your project to build. Because of Go’s built-in concurrency features, your software will scale to use the resources available without forcing you to use special threading libraries. Go uses a simple and effective type system that takes much of the overhead out of object-oriented development and lets you focus on code reuse. Go also has a garbage collector, so you don’t have to manage your own memory. Let’s look quickly at these key features.

1.1.1. Development speed

Compiling a large application in C or C++ takes more time than getting a cup of coffee. Figure 1.1 shows an XKCD classic excuse for messing around in the office.

Figure 1.1. Working hard? (via XKCD)

Go offers lightning-quick compiles by using a smart compiler and simplified dependency resolution algorithms. When you build a Go program, the compiler only needs to look at the libraries that you directly include, rather than traversing the dependencies of all the libraries that are included in the entire dependency chain like Java, C, and C++. Consequently, many Go applications compile in under a second. The entire Go source tree compiles in under 20 seconds on modern hardware.

Writing applications in dynamic languages makes you productive quickly because there are no intermediate steps between writing code and executing it. The trade-off is that dynamic languages don’t offer the type safety that static languages do and often need a comprehensive test suite to avoid discovering incorrect type bugs at runtime.

Imagine writing a large application in a dynamic language like JavaScript and coming across a function that expects to receive a field called ID. Is that an integer, a string, or a UUID? The way to find out is to look at the source. You could try to execute the function with a number or a string and see what happens. In Go, you wouldn’t spend time wondering, because the compiler will catch type differences for you.

1.1.2. Concurrency

One of the hardest things to do as a programmer is to write an application that effectively uses the available resources of the hardware running it. Modern computers have many cores, but most programming languages don’t have effective tools for utilizing those additional resources easily. They often require a lot of thread synchronization code, which is prone to errors.

Go’s concurrency support is one of its strongest features. Goroutines are like threads, but use far less memory and require less code to use. Channels are data structures that let you send typed messages between goroutines with synchronization built in. This facilitates a programming model where you send data between goroutines, rather than letting the goroutines fight to use the same data. Let’s look at these features in more detail now.

Goroutines

Goroutines are functions that run concurrently with other goroutines, including the entry point of your program. In other languages, you’d use threads to accomplish the same thing, but in Go many goroutines execute on a single thread. For example, if you write a web server and you want to handle different web requests simultaneously, you’d have to write a lot of extra code to use threads in C or Java. In Go, the net/http library has concurrency built in using goroutines. Each inbound request automatically runs on its own goroutine. Goroutines use less memory than threads and the Go runtime will automatically schedule the execution of goroutines against a set of configured logical processors. Each logical processor is bound to a single OS thread (see figure 1.2). This makes your application much more efficient with significantly less development effort.

Figure 1.2. Many goroutines execute on a single OS thread

If you want to execute some code concurrently while you move on to accomplish other things, a goroutine is perfect for the job. Here’s a quick example:

func log(msg string){ ... some logging code here } // Elsewhere in our code after we've discovered an error. go log("something dire happened")

That keyword go is all you need to schedule the log function to run as a goroutine and for that goroutine be run concurrently with other goroutines. This means you can continue executing the rest of your application while the logging happens concurrently, which often results in greater perceived performance for your end users. As stated before, goroutines have minimal overhead, so it isn’t uncommon to spawn tens of thousands of them. We’ll explore goroutines and concurrency more in-depth in chapter 6.

Channels

Channels are data structures that enable safe data communication between goroutines. Channels help you to avoid problems typically seen in programming languages that allow shared memory access.

The hardest part of concurrency is ensuring that your data isn’t unexpectedly modified by concurrently running processes, threads, or goroutines. When multiple threads change the same data without locks or synchronization, heartache always follows. In other languages, when you have global variables and shared memory, you’re required to use complicated locking disciplines to prevent unsynchronized changes to the same variables.

Channels help to solve this problem by providing a pattern that makes data safe from concurrent modification. Channels help to enforce t...