book

Learning Go

by Jon Bodner

March 2021

Beginner

375 pages

8h 59m

English

O'Reilly Media, Inc.

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Who Should Read This BookConventions Used in This BookUsing Code ExamplesO’Reilly Online LearningHow to Contact UsAcknowledgments
Installing the Go ToolsThe Go WorkspaceThe go Commandgo run and go buildGetting Third-Party Go ToolsFormatting Your CodeLinting and VettingChoose Your ToolsVisual Studio CodeGoLandThe Go PlaygroundMakefilesStaying Up to DateWrapping Up
Built-in TypesThe Zero ValueLiteralsBooleansNumeric TypesA Taste of Strings and RunesExplicit Type Conversionvar Versus :=Using constTyped and Untyped ConstantsUnused VariablesNaming Variables and ConstantsWrapping Up
Arrays—Too Rigid to Use DirectlySliceslenappendCapacitymakeDeclaring Your SliceSlicing SlicesConverting Arrays to SlicescopyStrings and Runes and BytesMapsReading and Writing a MapThe comma ok IdiomDeleting from MapsUsing Maps as SetsStructsAnonymous StructsComparing and Converting StructsWrapping Up
BlocksShadowing VariablesDetecting Shadowed Variablesif for, Four WaysThe Complete for StatementThe Condition-Only for StatementThe Infinite for Statementbreak and continueThe for-range StatementLabeling Your for StatementsChoosing the Right for StatementswitchBlank SwitchesChoosing Between if and switchgoto—Yes, gotoWrapping Up
Declaring and Calling FunctionsSimulating Named and Optional ParametersVariadic Input Parameters and SlicesMultiple Return ValuesMultiple Return Values Are Multiple ValuesIgnoring Returned ValuesNamed Return ValuesBlank Returns—Never Use These!Functions Are ValuesFunction Type DeclarationsAnonymous FunctionsClosuresPassing Functions as ParametersReturning Functions from FunctionsdeferGo Is Call By ValueWrapping Up
A Quick Pointer PrimerDon’t Fear the PointersPointers Indicate Mutable ParametersPointers Are a Last ResortPointer Passing PerformanceThe Zero Value Versus No ValueThe Difference Between Maps and SlicesSlices as BuffersReducing the Garbage Collector’s WorkloadWrapping Up
Types in GoMethodsPointer Receivers and Value ReceiversCode Your Methods for nil InstancesMethods Are Functions TooFunctions Versus MethodsType Declarations Aren’t InheritanceTypes Are Executable Documentationiota Is for Enumerations—SometimesUse Embedding for CompositionEmbedding Is Not InheritanceA Quick Lesson on InterfacesInterfaces Are Type-Safe Duck TypingEmbedding and InterfacesAccept Interfaces, Return StructsInterfaces and nilThe Empty Interface Says NothingType Assertions and Type SwitchesUse Type Assertions and Type Switches SparinglyFunction Types Are a Bridge to InterfacesImplicit Interfaces Make Dependency Injection EasierWireGo Isn’t Particularly Object-Oriented (and That’s Great)Wrapping Up
How to Handle Errors: The BasicsUse Strings for Simple ErrorsSentinel ErrorsErrors Are ValuesWrapping ErrorsIs and AsWrapping Errors with deferpanic and recoverGetting a Stack Trace from an ErrorWrapping Up
Repositories, Modules, and Packagesgo.modBuilding PackagesImports and ExportsCreating and Accessing a PackageNaming PackagesHow to Organize Your ModuleOverriding a Package’s NamePackage Comments and godocThe internal PackageThe init Function: Avoid if PossibleCircular DependenciesGracefully Renaming and Reorganizing Your APIWorking with ModulesImporting Third-Party CodeWorking with VersionsMinimal Version SelectionUpdating to Compatible VersionsUpdating to Incompatible VersionsVendoringpkg.go.devAdditional InformationPublishing Your ModuleVersioning Your ModuleModule Proxy ServersSpecifying a Proxy ServerPrivate RepositoriesWrapping Up

When to Use ConcurrencyGoroutinesChannelsReading, Writing, and Bufferingfor-range and ChannelsClosing a ChannelHow Channels BehaveselectConcurrency Practices and PatternsKeep Your APIs Concurrency-FreeGoroutines, for Loops, and Varying VariablesAlways Clean Up Your GoroutinesThe Done Channel PatternUsing a Cancel Function to Terminate a GoroutineWhen to Use Buffered and Unbuffered ChannelsBackpressureTurning Off a case in a selectHow to Time Out CodeUsing WaitGroupsRunning Code Exactly OncePutting Our Concurrent Tools TogetherWhen to Use Mutexes Instead of ChannelsAtomics—You Probably Don’t Need TheseWhere to Learn More About ConcurrencyWrapping Up
io and FriendstimeMonotonic TimeTimers and Timeoutsencoding/jsonUse Struct Tags to Add MetadataUnmarshaling and MarshalingJSON, Readers, and WritersEncoding and Decoding JSON StreamsCustom JSON Parsingnet/httpThe ClientThe ServerWrapping Up
What Is the Context?CancellationTimersHandling Context Cancellation in Your Own CodeValuesWrapping Up
The Basics of TestingReporting Test FailuresSetting Up and Tearing DownStoring Sample Test DataCaching Test ResultsTesting Your Public APIUse go-cmp to Compare Test ResultsTable TestsChecking Your Code CoverageBenchmarksStubs in GohttptestIntegration Tests and Build TagsFinding Concurrency Problems with the Race CheckerWrapping Up
Reflection Lets Us Work with Types at RuntimeTypes, Kinds, and ValuesMaking New ValuesUse Reflection to Check If an Interface’s Value Is nilUse Reflection to Write a Data MarshalerBuild Functions with Reflection to Automate Repetitive TasksYou Can Build Structs with Reflection, but Don’tReflection Can’t Make MethodsOnly Use Reflection If It’s Worthwhileunsafe Is UnsafeUse unsafe to Convert External Binary Dataunsafe Strings and Slicesunsafe ToolsCgo Is for Integration, Not PerformanceWrapping Up
Generics Reduce Repetitive Code and Increase Type SafetyIntroducing Generics in GoGeneric Functions Abstract AlgorithmsGenerics and InterfacesUse Type Terms to Specify OperatorsType Inference and GenericsType Elements Limit ConstantsCombining Generic Functions with Generic Data StructuresThings That Are Left OutIdiomatic Go and GenericsFurther Futures UnlockedWrapping Up

Content preview from Learning Go

Chapter 14. Here There Be Dragons: Reflect, Unsafe, and Cgo

The edges of the known world are scary. Ancient maps would fill in the unexplored areas with pictures of dragons and lions. In our previous sections, we have emphasized that Go is a safe language, with typed variables to make clear what sort of data you are using and garbage collection to manage memory. Even the pointers are tame; you can’t abuse them in the way that C and C++ do.

All of those things are true, and for the vast majority of the Go code that you’ll write, you can be assured that the Go runtime will protect you. But there are escape hatches. Sometimes your Go programs need to venture out into less defined areas. In this chapter, we’re going to look at how to handle situations that can’t be solved with normal Go code. For example, when the type of the data can’t be determined at compile time, you can use the reflection support in the reflect package to interact with and even construct data. When you need to take advantage of the memory layout of data types in Go, you can use the unsafe package. And if there is functionality that can only be provided by libraries written in C, you can call into C code with cgo.

You might be wondering why these advanced concepts appear in a book targeted at those new to Go. There are two reasons. First, developers searching for a solution to a problem sometimes discover (and copy and paste) techniques they don’t fully understand. It’s best to know a bit about advanced techniques ...