--- /dev/null
+// Copyright 2019 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.
+
+package label
+
+import (
+ "fmt"
+ "io"
+ "reflect"
+ "unsafe"
+)
+
+// Key is used as the identity of a Label.
+// Keys are intended to be compared by pointer only, the name should be unique
+// for communicating with external systems, but it is not required or enforced.
+type Key interface {
+ // Name returns the key name.
+ Name() string
+ // Description returns a string that can be used to describe the value.
+ Description() string
+
+ // Format is used in formatting to append the value of the label to the
+ // supplied buffer.
+ // The formatter may use the supplied buf as a scratch area to avoid
+ // allocations.
+ Format(w io.Writer, buf []byte, l Label)
+}
+
+// Label holds a key and value pair.
+// It is normally used when passing around lists of labels.
+type Label struct {
+ key Key
+ packed uint64
+ untyped interface{}
+}
+
+// Map is the interface to a collection of Labels indexed by key.
+type Map interface {
+ // Find returns the label that matches the supplied key.
+ Find(key Key) Label
+}
+
+// List is the interface to something that provides an iterable
+// list of labels.
+// Iteration should start from 0 and continue until Valid returns false.
+type List interface {
+ // Valid returns true if the index is within range for the list.
+ // It does not imply the label at that index will itself be valid.
+ Valid(index int) bool
+ // Label returns the label at the given index.
+ Label(index int) Label
+}
+
+// list implements LabelList for a list of Labels.
+type list struct {
+ labels []Label
+}
+
+// filter wraps a LabelList filtering out specific labels.
+type filter struct {
+ keys []Key
+ underlying List
+}
+
+// listMap implements LabelMap for a simple list of labels.
+type listMap struct {
+ labels []Label
+}
+
+// mapChain implements LabelMap for a list of underlying LabelMap.
+type mapChain struct {
+ maps []Map
+}
+
+// OfValue creates a new label from the key and value.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func OfValue(k Key, value interface{}) Label { return Label{key: k, untyped: value} }
+
+// UnpackValue assumes the label was built using LabelOfValue and returns the value
+// that was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) UnpackValue() interface{} { return t.untyped }
+
+// Of64 creates a new label from a key and a uint64. This is often
+// used for non uint64 values that can be packed into a uint64.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func Of64(k Key, v uint64) Label { return Label{key: k, packed: v} }
+
+// Unpack64 assumes the label was built using LabelOf64 and returns the value that
+// was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) Unpack64() uint64 { return t.packed }
+
+// OfString creates a new label from a key and a string.
+// This method is for implementing new key types, label creation should
+// normally be done with the Of method of the key.
+func OfString(k Key, v string) Label {
+ hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
+ return Label{
+ key: k,
+ packed: uint64(hdr.Len),
+ untyped: unsafe.Pointer(hdr.Data),
+ }
+}
+
+// UnpackString assumes the label was built using LabelOfString and returns the
+// value that was passed to that constructor.
+// This method is for implementing new key types, for type safety normal
+// access should be done with the From method of the key.
+func (t Label) UnpackString() string {
+ var v string
+ hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
+ hdr.Data = uintptr(t.untyped.(unsafe.Pointer))
+ hdr.Len = int(t.packed)
+ return *(*string)(unsafe.Pointer(hdr))
+}
+
+// Valid returns true if the Label is a valid one (it has a key).
+func (t Label) Valid() bool { return t.key != nil }
+
+// Key returns the key of this Label.
+func (t Label) Key() Key { return t.key }
+
+// Format is used for debug printing of labels.
+func (t Label) Format(f fmt.State, r rune) {
+ if !t.Valid() {
+ io.WriteString(f, `nil`)
+ return
+ }
+ io.WriteString(f, t.Key().Name())
+ io.WriteString(f, "=")
+ var buf [128]byte
+ t.Key().Format(f, buf[:0], t)
+}
+
+func (l *list) Valid(index int) bool {
+ return index >= 0 && index < len(l.labels)
+}
+
+func (l *list) Label(index int) Label {
+ return l.labels[index]
+}
+
+func (f *filter) Valid(index int) bool {
+ return f.underlying.Valid(index)
+}
+
+func (f *filter) Label(index int) Label {
+ l := f.underlying.Label(index)
+ for _, f := range f.keys {
+ if l.Key() == f {
+ return Label{}
+ }
+ }
+ return l
+}
+
+func (lm listMap) Find(key Key) Label {
+ for _, l := range lm.labels {
+ if l.Key() == key {
+ return l
+ }
+ }
+ return Label{}
+}
+
+func (c mapChain) Find(key Key) Label {
+ for _, src := range c.maps {
+ l := src.Find(key)
+ if l.Valid() {
+ return l
+ }
+ }
+ return Label{}
+}
+
+var emptyList = &list{}
+
+func NewList(labels ...Label) List {
+ if len(labels) == 0 {
+ return emptyList
+ }
+ return &list{labels: labels}
+}
+
+func Filter(l List, keys ...Key) List {
+ if len(keys) == 0 {
+ return l
+ }
+ return &filter{keys: keys, underlying: l}
+}
+
+func NewMap(labels ...Label) Map {
+ return listMap{labels: labels}
+}
+
+func MergeMaps(srcs ...Map) Map {
+ var nonNil []Map
+ for _, src := range srcs {
+ if src != nil {
+ nonNil = append(nonNil, src)
+ }
+ }
+ if len(nonNil) == 1 {
+ return nonNil[0]
+ }
+ return mapChain{maps: nonNil}
+}
projects / dotfiles / .git / blobdiff