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/*
*
* Copyright 2019 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
// Package attributes defines a generic key/value store used in various gRPC
// components.
//
// # Experimental
//
// Notice: This package is EXPERIMENTAL and may be changed or removed in a
// later release.
package attributes
import (
"fmt"
"strings"
)
// Attributes is an immutable struct for storing and retrieving generic
// key/value pairs. Keys must be hashable, and users should define their own
// types for keys. Values should not be modified after they are added to an
// Attributes or if they were received from one. If values implement 'Equal(o
// interface{}) bool', it will be called by (*Attributes).Equal to determine
// whether two values with the same key should be considered equal.
type Attributes struct {
m map[interface{}]interface{}
}
// New returns a new Attributes containing the key/value pair.
func New(key, value interface{}) *Attributes {
return &Attributes{m: map[interface{}]interface{}{key: value}}
}
// WithValue returns a new Attributes containing the previous keys and values
// and the new key/value pair. If the same key appears multiple times, the
// last value overwrites all previous values for that key. To remove an
// existing key, use a nil value. value should not be modified later.
func (a *Attributes) WithValue(key, value interface{}) *Attributes {
if a == nil {
return New(key, value)
}
n := &Attributes{m: make(map[interface{}]interface{}, len(a.m)+1)}
for k, v := range a.m {
n.m[k] = v
}
n.m[key] = value
return n
}
// Value returns the value associated with these attributes for key, or nil if
// no value is associated with key. The returned value should not be modified.
func (a *Attributes) Value(key interface{}) interface{} {
if a == nil {
return nil
}
return a.m[key]
}
// Equal returns whether a and o are equivalent. If 'Equal(o interface{})
// bool' is implemented for a value in the attributes, it is called to
// determine if the value matches the one stored in the other attributes. If
// Equal is not implemented, standard equality is used to determine if the two
// values are equal. Note that some types (e.g. maps) aren't comparable by
// default, so they must be wrapped in a struct, or in an alias type, with Equal
// defined.
func (a *Attributes) Equal(o *Attributes) bool {
if a == nil && o == nil {
return true
}
if a == nil || o == nil {
return false
}
if len(a.m) != len(o.m) {
return false
}
for k, v := range a.m {
ov, ok := o.m[k]
if !ok {
// o missing element of a
return false
}
if eq, ok := v.(interface{ Equal(o interface{}) bool }); ok {
if !eq.Equal(ov) {
return false
}
} else if v != ov {
// Fallback to a standard equality check if Value is unimplemented.
return false
}
}
return true
}
// String prints the attribute map. If any key or values throughout the map
// implement fmt.Stringer, it calls that method and appends.
func (a *Attributes) String() string {
var sb strings.Builder
sb.WriteString("{")
first := true
for k, v := range a.m {
var key, val string
if str, ok := k.(interface{ String() string }); ok {
key = str.String()
}
if str, ok := v.(interface{ String() string }); ok {
val = str.String()
}
if !first {
sb.WriteString(", ")
}
sb.WriteString(fmt.Sprintf("%q: %q, ", key, val))
first = false
}
sb.WriteString("}")
return sb.String()
}
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