Golang，context.TODO 会不会出错

Question

ctx = context.TODO()cmd := exec.CommandContext(ctx, <some_cmd>, <some_arg>)fmt.Println(ctx.Err())ctx.Err() 是否会在 ctx 为 context.TODO() 时变为非零？

Answer 1

context.TODO().Err() 将始终返回 nil，这在源代码中很容易看出：

package context

// An emptyCtx is never canceled, has no values, and has no deadline.

type emptyCtx int

func (*emptyCtx) Err() error {

    return nil

}

// ...

var (

    todo       = new(emptyCtx)

)

// ...

// TODO returns a non-nil, empty Context. Code should use context.TODO when

// it's unclear which Context to use or it is not yet available (because the

// surrounding function has not yet been extended to accept a Context

// parameter).

func TODO() Context {

    return todo

}