上下文接口设计

这是

context.Context

type Context interface {    Deadline() (deadline time.Time, ok bool)    Done() <-chan struct{}    Err() error    Value(key interface{}) interface{}}

这很简单。如果要编写它的实现，可以这样做吗？是的，很容易。由于没有“设置”方法，因此每个方法都只能返回默认值/
零值，并且是“有效”的实现。这正是背景和TODO上下文（

context.Background()

context.TODO()

如果您要添加从现有环境（例如，等） 派生
新上下文的功能作为接口本身的一部分，则将需要为所有人提供（有效）实现，这是不可行的；而且几乎不需要同时使用它们，因此这会浪费资源。

context.WithCancel()

context.WithDeadline()

Context

扩展负责添加实现。如果您查看

context

context/context.go

context.Context

// An emptyCtx is never canceled, has no values, and has no deadline. It is not// struct{}, since vars of this type must have distinct addresses.type emptyCtx int// A cancelCtx can be canceled. When canceled, it also cancels any children// that implement canceler.type cancelCtx struct {    Context    done chan struct{} // closed by the first cancel call.    mu       sync.Mutex    children map[canceler]bool // set to nil by the first cancel call    err      error  // set to non-nil by the first cancel call}// A timerCtx carries a timer and a deadline. It embeds a cancelCtx to// implement Done and Err. It implements cancel by stopping its timer then// delegating to cancelCtx.cancel.type timerCtx struct {    cancelCtx    timer *time.Timer // Under cancelCtx.mu.    deadline time.Time}// A valueCtx carries a key-value pair. It implements Value for that key and// delegates all other calls to the embedded Context.type valueCtx struct {    Context    key, val interface{}}

显然，我们可以弥补软件包

context.Context

context

Context