48 - Build Constraints and Tags

Conditional compilation for different platforms and build configurations.

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📌 What You'll Learn

• Build constraints (build tags)
• Platform-specific code
• Custom build tags
• go:generate directive

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🔧 Build Constraints

Build constraints = Compile code conditionally

Use Case	Example
Platform-specific	Windows vs Linux
Architecture-specific	amd64 vs arm
Build modes	debug vs release
Optional features	Custom tags

Two ways to specify:

1. File naming: file_linux.go, file_windows.go, file_darwin.go
2. //go:build directive: //go:build linux && amd64

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📝 Platform-Specific Code

// main.go - shared code
package main
func main() {
    println(getSystemInfo())
}

// system_linux.go
//go:build linux
package main
func getSystemInfo() string { return "Running on Linux" }

// system_darwin.go
//go:build darwin
package main
func getSystemInfo() string { return "Running on macOS" }

// system_windows.go
//go:build windows
package main
func getSystemInfo() string { return "Running on Windows" }

Output: Varies by GOOS build target (e.g., "Running on Linux")

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🏷️ Build Tags Syntax

//go:build linux
//go:build linux || darwin
//go:build linux && amd64
//go:build !windows
//go:build (linux || darwin) && amd64
//go:build debug

go build
go build -tags debug
go build -tags "debug integration"
GOOS=linux go build
GOOS=windows GOARCH=amd64 go build

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🎭 Debug vs Release

// debug.go
//go:build debug
package main
func debugLog(msg string) { log.Printf("[DEBUG] %s\n", msg) }
const DebugMode = true

// release.go
//go:build !debug
package main
func debugLog(msg string) {}
const DebugMode = false

go build -tags debug -o myapp-debug
go build -o myapp

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⚙️ go:generate

//go:generate stringer -type=Status
//go:generate mockgen -source=interface.go -destination=mock_interface.go

go generate ./...
go generate generate.go

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📂 File Naming Conventions

Pattern	Example	When compiled
*_GOOS.go	file_linux.go	Linux only
*_GOARCH.go	file_amd64.go	amd64 only
*_GOOS_GOARCH.go	file_linux_amd64.go	Linux amd64 only
*_test.go	server_test.go	Test build only

Common values: GOOS: linux, darwin, windows | GOARCH: amd64, arm64, arm, 386

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🎯 Key Takeaways

1. //go:build for compile-time constraints
2. File naming (_linux.go) for platform code
3. Custom tags with -tags flag
4. go generate for code generation
5. GOOS/GOARCH for cross-compilation

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➡️ Next Steps

Next Topic: 49 - Module Management