ctxkey

ctxkey/ctxkey.go

@@ -0,0 +1,49 @@
+// Package ctxkey is like errors.New() for context keys.
+//
+// Origin: https://github.com/cstockton/pkg/tree/master/ctxkey
+//
+// # Invariants
+//
+// All context keys created with New() will be globally unique during program
+// execution for the lifespan of the Key and will not cause additional
+// allocations when they are associated with a context value. Uniqueness is
+// satisfied by returning pointers to a private key struct, forcing comparison
+// operations in context value retrieval to use pointer equality within the
+// current Go's specification:
+//
+//  https://golang.org/ref/spec#Comparison_operators
+//
+// Additional allocations means that you will not allocate for the context key
+// as seen with this common idiom:
+//
+//  type key int
+//  var myKey key = 0
+//  // 3 allocations, context struct, myKey and someValue
+//  context.WithValue(ctx, myKey, SomeValue)
+//
+// Keys issued by New() fit within an interface{} value, i.e.:
+//
+//  var myKey = ctxkey.New(`MyKey`)
+//  // 2 allocations, context struct and someValue
+//  context.WithValue(ctx, myKey, SomeValue)
+package ctxkey
+
+import (
+	"fmt"
+)
+
+type Key interface {
+	fmt.Stringer
+}
+
+type key struct {
+	name string
+}
+
+func New(name string) Key {
+	return &key{name}
+}
+
+func (k key) String() string {
+	return `ctxkey "` + k.name + `"`
+}

ctxkey/ctxkey_test.go

@@ -0,0 +1,22 @@
+package ctxkey_test
+
+import (
+	"context"
+	"testing"
+
+	. "github.com/nbgrp/pkg/ctxkey"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCtxkey(t *testing.T) {
+	t.Parallel()
+
+	key := New("testkey")
+	val := "testvalue"
+	ctx := context.WithValue(context.Background(), key, val)
+
+	assert.Equal(t, ctx.Value(key), val)
+	assert.Nil(t, ctx.Value("testkey"))
+
+	assert.Equal(t, `ctxkey "testkey"`, key.String())
+}

ctxkey/go.mod

@@ -0,0 +1,5 @@
+module github.com/nbgrp/pkg/ctxkey
+
+go 1.14
+
+require github.com/stretchr/testify v1.9.0

ctxkey/go.sum

@@ -0,0 +1,19 @@
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