是什麼：建立指令？

go:build是Go語言中用於控制源文件參與構建的條件編譯指令，使用時需置於Go文件頂部，緊接包聲明之後或代碼之前，語法為//go:build condition且不能有空格。 1. 它根據指定條件決定是否包含該文件，如//go:build linux表示僅在構建Linux時包含；2. 支持邏輯非、與、或操作，例如!windows、linux,amd64或linux || darwin；3. 常用於平台相關代碼管理，如區分file_linux.go和file_windows.go；4. 與舊版build註釋相比，go:build採用標準布爾表達式，規則更清晰；5. 注意多個條件組合時括號會影響邏輯判斷，且空格會導致指令被忽略。

The go:build directive is a special comment you can include in Go source files to control which builds the file should be included in. It's not a package-level thing, just a per-file control mechanism.

How to Use go:build

You place it at the top of your Go file, right after the package declaration or before any code. The syntax looks like this:

 //go:build condition

It's important to note that there's no space between //go: and build . This line tells the Go toolchain whether to include this file when building for a certain target.

For example:

 //go:build linux

This means the file will only be included when building for Linux.

You can also use negation:

Which means "include this file if it's not Windows".

And combine conditions:

Or with OR logic:

Common Use Cases

You typically use go:build directives when writing platform-specific code — for example, different implementations for different operating systems or architectures.

Some typical scenarios:

• You have a file_linux.go and a file_windows.go , both implementing the same interface but with OS-specific behavior.
• You want to exclude certain tests or benchmarks from running on specific platforms.
• You're maintaining alternative implementations for performance or compatibility reasons.

This helps keep your codebase clean by separating concerns based on build targets without needing complex directory structures.

Differences from build Comments

Before Go 1.17, people used the older build comment format:

 // build linux

That still works, but the new go:build syntax has better semantics and clearer evaluation rules. One key difference is that go:build uses standard boolean expressions, while build had more implicit logic and required blank lines around it.

If you're starting fresh or updating old code, it's recommended to go with go:build .

A Few Things to Watch Out For

There are a few gotchas to be aware of:

• Make sure there's no space in //go:build — otherwise, it gets ignored silently.
• It only affects file inclusion at build time; it doesn't impact test runs unless you're using -run or similar flags that might change how files are selected.
• If you're using multiple directives in one file, they all must evaluate to true for the file to be included.

Also, when combining conditions, parentheses matter:

is different from

So be precise about what you're targeting.

基本上就這些。

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