event: add Label.Apply
Expose the dispatch functionality via an exported method.
Change-Id: If01385a9357790d713a9256c61e2bbfdd1766f16
Reviewed-on: https://go-review.googlesource.com/c/exp/+/311454
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
diff --git a/event/label.go b/event/label.go
index b1cb46e..d867dd4 100644
--- a/event/label.go
+++ b/event/label.go
@@ -5,7 +5,9 @@
package event
import (
+ "fmt"
"reflect"
+ "strconv"
"unsafe"
)
@@ -90,3 +92,49 @@
// Key returns the key of this Label.
func (l Label) Key() string { return l.key }
+
+// Apply calls the appropriate method of h on the label's value.
+func (l Label) Apply(h ValueHandler) {
+ if l.dispatch != nil {
+ l.dispatch(h, l)
+ }
+}
+
+//////////////////////////////////////////////////////////////////////
+
+// These are more demos of what Apply can do, rather than things we'd
+// necessarily want here.
+
+// Value is an expensive but general way to get a label's value.
+func (l Label) Value() interface{} {
+ var v interface{}
+ l.Apply(vhandler{&v})
+ return v
+}
+
+type vhandler struct {
+ pv *interface{}
+}
+
+func (h vhandler) String(v string) { *h.pv = v }
+func (h vhandler) Quote(v string) { *h.pv = strconv.Quote(v) }
+func (h vhandler) Int(v int64) { *h.pv = v }
+func (h vhandler) Uint(v uint64) { *h.pv = v }
+func (h vhandler) Float(v float64) { *h.pv = v }
+func (h vhandler) Value(v interface{}) { *h.pv = v }
+
+// AppendValue appends the value of l to *dst as text.
+func (l Label) AppendValue(dst *[]byte) {
+ l.Apply(ahandler{dst})
+}
+
+type ahandler struct {
+ b *[]byte
+}
+
+func (h ahandler) String(v string) { *h.b = append(*h.b, v...) }
+func (h ahandler) Quote(v string) { *h.b = strconv.AppendQuote(*h.b, v) }
+func (h ahandler) Int(v int64) { *h.b = strconv.AppendInt(*h.b, v, 10) }
+func (h ahandler) Uint(v uint64) { *h.b = strconv.AppendUint(*h.b, v, 10) }
+func (h ahandler) Float(v float64) { *h.b = strconv.AppendFloat(*h.b, v, 'E', -1, 32) }
+func (h ahandler) Value(v interface{}) { *h.b = append(*h.b, fmt.Sprint(v)...) }
