context.go
func From(ctx context.Context) Context {
	if c, ok := ctx.(Context); ok {
		return c
	}
	return &contextT{ctx: ctx}
}
func From(ctx context.Context) Context {
	if c, ok := ctx.(Context); ok {
		return c
	}
	return &contextT{ctx: ctx}
}
// From creates a new context based on ctx. See the Context example.