context: use Go 1.8 type alias for CancelFunc and Context
CancelFunc was the only part of the context package which didn't
forward nicely with the move from x/net/context to std context.
Use it for Context as well.
Change-Id: Ieff39b10b0783d55d0437c73923053297ed0ea4a
Reviewed-on: https://go-review.googlesource.com/32317
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/context/context.go b/context/context.go
index 134654c..d1ed420 100644
--- a/context/context.go
+++ b/context/context.go
@@ -36,103 +36,6 @@
// Contexts.
package context // import "golang.org/x/net/context"
-import "time"
-
-// A Context carries a deadline, a cancelation signal, and other values across
-// API boundaries.
-//
-// Context's methods may be called by multiple goroutines simultaneously.
-type Context interface {
- // Deadline returns the time when work done on behalf of this context
- // should be canceled. Deadline returns ok==false when no deadline is
- // set. Successive calls to Deadline return the same results.
- Deadline() (deadline time.Time, ok bool)
-
- // Done returns a channel that's closed when work done on behalf of this
- // context should be canceled. Done may return nil if this context can
- // never be canceled. Successive calls to Done return the same value.
- //
- // WithCancel arranges for Done to be closed when cancel is called;
- // WithDeadline arranges for Done to be closed when the deadline
- // expires; WithTimeout arranges for Done to be closed when the timeout
- // elapses.
- //
- // Done is provided for use in select statements:
- //
- // // Stream generates values with DoSomething and sends them to out
- // // until DoSomething returns an error or ctx.Done is closed.
- // func Stream(ctx context.Context, out chan<- Value) error {
- // for {
- // v, err := DoSomething(ctx)
- // if err != nil {
- // return err
- // }
- // select {
- // case <-ctx.Done():
- // return ctx.Err()
- // case out <- v:
- // }
- // }
- // }
- //
- // See http://blog.golang.org/pipelines for more examples of how to use
- // a Done channel for cancelation.
- Done() <-chan struct{}
-
- // Err returns a non-nil error value after Done is closed. Err returns
- // Canceled if the context was canceled or DeadlineExceeded if the
- // context's deadline passed. No other values for Err are defined.
- // After Done is closed, successive calls to Err return the same value.
- Err() error
-
- // Value returns the value associated with this context for key, or nil
- // if no value is associated with key. Successive calls to Value with
- // the same key returns the same result.
- //
- // Use context values only for request-scoped data that transits
- // processes and API boundaries, not for passing optional parameters to
- // functions.
- //
- // A key identifies a specific value in a Context. Functions that wish
- // to store values in Context typically allocate a key in a global
- // variable then use that key as the argument to context.WithValue and
- // Context.Value. A key can be any type that supports equality;
- // packages should define keys as an unexported type to avoid
- // collisions.
- //
- // Packages that define a Context key should provide type-safe accessors
- // for the values stores using that key:
- //
- // // Package user defines a User type that's stored in Contexts.
- // package user
- //
- // import "golang.org/x/net/context"
- //
- // // User is the type of value stored in the Contexts.
- // type User struct {...}
- //
- // // key is an unexported type for keys defined in this package.
- // // This prevents collisions with keys defined in other packages.
- // type key int
- //
- // // userKey is the key for user.User values in Contexts. It is
- // // unexported; clients use user.NewContext and user.FromContext
- // // instead of using this key directly.
- // var userKey key = 0
- //
- // // NewContext returns a new Context that carries value u.
- // func NewContext(ctx context.Context, u *User) context.Context {
- // return context.WithValue(ctx, userKey, u)
- // }
- //
- // // FromContext returns the User value stored in ctx, if any.
- // func FromContext(ctx context.Context) (*User, bool) {
- // u, ok := ctx.Value(userKey).(*User)
- // return u, ok
- // }
- Value(key interface{}) interface{}
-}
-
// Background returns a non-nil, empty Context. It is never canceled, has no
// values, and has no deadline. It is typically used by the main function,
// initialization, and tests, and as the top-level Context for incoming
@@ -149,8 +52,3 @@
func TODO() Context {
return todo
}
-
-// A CancelFunc tells an operation to abandon its work.
-// A CancelFunc does not wait for the work to stop.
-// After the first call, subsequent calls to a CancelFunc do nothing.
-type CancelFunc func()
diff --git a/context/go18.go b/context/go18.go
new file mode 100644
index 0000000..35360c5
--- /dev/null
+++ b/context/go18.go
@@ -0,0 +1,22 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.8
+
+package context
+
+import (
+ "context" // standard library's context, as of Go 1.7
+)
+
+// A Context carries a deadline, a cancelation signal, and other values across
+// API boundaries.
+//
+// Context's methods may be called by multiple goroutines simultaneously.
+type Context => context.Context
+
+// A CancelFunc tells an operation to abandon its work.
+// A CancelFunc does not wait for the work to stop.
+// After the first call, subsequent calls to a CancelFunc do nothing.
+type CancelFunc => context.CancelFunc
diff --git a/context/pre_go18.go b/context/pre_go18.go
new file mode 100644
index 0000000..41bd8ba
--- /dev/null
+++ b/context/pre_go18.go
@@ -0,0 +1,109 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !go1.8
+
+package context
+
+import "time"
+
+// A CancelFunc tells an operation to abandon its work.
+// A CancelFunc does not wait for the work to stop.
+// After the first call, subsequent calls to a CancelFunc do nothing.
+type CancelFunc func()
+
+// A Context carries a deadline, a cancelation signal, and other values across
+// API boundaries.
+//
+// Context's methods may be called by multiple goroutines simultaneously.
+type Context interface {
+ // Deadline returns the time when work done on behalf of this context
+ // should be canceled. Deadline returns ok==false when no deadline is
+ // set. Successive calls to Deadline return the same results.
+ Deadline() (deadline time.Time, ok bool)
+
+ // Done returns a channel that's closed when work done on behalf of this
+ // context should be canceled. Done may return nil if this context can
+ // never be canceled. Successive calls to Done return the same value.
+ //
+ // WithCancel arranges for Done to be closed when cancel is called;
+ // WithDeadline arranges for Done to be closed when the deadline
+ // expires; WithTimeout arranges for Done to be closed when the timeout
+ // elapses.
+ //
+ // Done is provided for use in select statements:
+ //
+ // // Stream generates values with DoSomething and sends them to out
+ // // until DoSomething returns an error or ctx.Done is closed.
+ // func Stream(ctx context.Context, out chan<- Value) error {
+ // for {
+ // v, err := DoSomething(ctx)
+ // if err != nil {
+ // return err
+ // }
+ // select {
+ // case <-ctx.Done():
+ // return ctx.Err()
+ // case out <- v:
+ // }
+ // }
+ // }
+ //
+ // See http://blog.golang.org/pipelines for more examples of how to use
+ // a Done channel for cancelation.
+ Done() <-chan struct{}
+
+ // Err returns a non-nil error value after Done is closed. Err returns
+ // Canceled if the context was canceled or DeadlineExceeded if the
+ // context's deadline passed. No other values for Err are defined.
+ // After Done is closed, successive calls to Err return the same value.
+ Err() error
+
+ // Value returns the value associated with this context for key, or nil
+ // if no value is associated with key. Successive calls to Value with
+ // the same key returns the same result.
+ //
+ // Use context values only for request-scoped data that transits
+ // processes and API boundaries, not for passing optional parameters to
+ // functions.
+ //
+ // A key identifies a specific value in a Context. Functions that wish
+ // to store values in Context typically allocate a key in a global
+ // variable then use that key as the argument to context.WithValue and
+ // Context.Value. A key can be any type that supports equality;
+ // packages should define keys as an unexported type to avoid
+ // collisions.
+ //
+ // Packages that define a Context key should provide type-safe accessors
+ // for the values stores using that key:
+ //
+ // // Package user defines a User type that's stored in Contexts.
+ // package user
+ //
+ // import "golang.org/x/net/context"
+ //
+ // // User is the type of value stored in the Contexts.
+ // type User struct {...}
+ //
+ // // key is an unexported type for keys defined in this package.
+ // // This prevents collisions with keys defined in other packages.
+ // type key int
+ //
+ // // userKey is the key for user.User values in Contexts. It is
+ // // unexported; clients use user.NewContext and user.FromContext
+ // // instead of using this key directly.
+ // var userKey key = 0
+ //
+ // // NewContext returns a new Context that carries value u.
+ // func NewContext(ctx context.Context, u *User) context.Context {
+ // return context.WithValue(ctx, userKey, u)
+ // }
+ //
+ // // FromContext returns the User value stored in ctx, if any.
+ // func FromContext(ctx context.Context) (*User, bool) {
+ // u, ok := ctx.Value(userKey).(*User)
+ // return u, ok
+ // }
+ Value(key interface{}) interface{}
+}
