Breaking: replace key value pairs with slog.Attrs (#27)

* Breaking: replace key value pairs with slog.Attrs

* Format README.md

* Use slices.Concat

Author: FollowTheProcess

README.md

@@ -34,6 +34,7 @@ package main
 import (
     "fmt"
     "os"
+    "log/slog"
 
     "go.followtheprocess.codes/log"
 )
@@ -42,7 +43,11 @@ func main() {
     logger := log.New(os.Stderr)
 
     logger.Debug("Debug me") // By default this one won't show up, default log level is INFO
-    logger.Info("Some information here", "really", true)
+    logger.Info(
+      "Some information here",
+      // Yep! You use slog.Attrs for key value pairs, why reinvent the wheel?
+      slog.Bool("really", true),
+    )
     logger.Warn("Uh oh!")
     logger.Error("Goodbye")
 }
@@ -84,18 +89,24 @@ logger := log.New(os.Stderr, log.WithLevel(log.LevelDebug))
 
 ### Key Value Pairs
 
-`log` provides "semi structured" logs in that the message is free form text but you can attach arbitrary key value pairs to any of the log methods
+`log` uses [slog.Attr] to provide "semi structured" logs. The message is free form text but you can attach arbitrary key, value pairs with any of the log methods
 
 ```go
-logger.Info("Doing something", "cache", true, "duration", 30 * time.Second, "number", 42)
+logger.Info(
+ "Doing something",
+ slog.Bool("cache", true),
+ slog.Duration("duration", 30 * time.Second),
+ slog.Int("number", 42),
+)
 ```
 
 You can also create a "sub logger" with persistent key value pairs applied to every message
 
 ```go
-sub := logger.With("sub", true)
+sub := logger.With(slog.Bool("sub", true))
 
-sub.Info("Hello from the sub logger", "subkey", "yes") // They can have their own per-method keys too!
+// They can have their own per-method keys too!
+sub.Info("Hello from the sub logger", slog.String("subkey", "yes"))
 ```
 
 <p align="center">
@@ -120,3 +131,5 @@ prefixed := logger.Prefixed("http")
 <p align="center">
 <img src="https://github.com/FollowTheProcess/log/raw/main/docs/img/prefix.gif" alt="demo">
 </p>
+
+[slog.Attr]: https://pkg.go.dev/log/slog#Attr

docs/img/demo.gif

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"log/slog"
 	"math/rand/v2"
 	"os"
 	"time"
@@ -11,15 +12,23 @@ import (
 func main() {
 	logger := log.New(os.Stderr, log.WithLevel(log.LevelDebug))
 
-	logger.Debug("Searing steak", "cook", "rare", "temp", "42°C", "time", 2*time.Minute)
+	logger.Debug(
+		"Searing steak",
+		slog.String("cook", "rare"),
+		slog.Int("temp", 42),
+		slog.Duration("time", 2*time.Minute),
+	)
 	sleep()
-	logger.Info("Choosing wine pairing", "choices", []string{"merlot", "malbec", "rioja"})
+	logger.Info(
+		"Choosing wine pairing",
+		slog.Any("choices", []string{"merlot", "malbec", "rioja"}),
+	)
 	sleep()
 	logger.Error("No malbec left!")
 	sleep()
-	logger.Warn("Falling back to second choice", "fallback", "rioja")
+	logger.Warn("Falling back to second choice", slog.String("fallback", "rioja"))
 
-	logger.Info("Eating steak", "cut", "sirloin", "enjoying", true)
+	logger.Info("Eating steak", slog.String("cut", "sirloin"), slog.Bool("enjoying", true))
 }
 
 func sleep() {

docs/img/keys.gif

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"log/slog"
 	"math/rand/v2"
 	"os"
 	"time"
@@ -11,11 +12,16 @@ import (
 func main() {
 	logger := log.New(os.Stderr, log.WithLevel(log.LevelDebug))
 
-	logger.Info("Doing something", "cache", true, "duration", 30*time.Second, "number", 42)
+	logger.Info(
+		"Doing something",
+		slog.Bool("cache", true),
+		slog.Duration("duration", 30*time.Second),
+		slog.Int("number", 42),
+	)
 	sleep()
 
-	sub := logger.With("sub", true)
-	sub.Info("Hello from the sub logger", "subkey", "yes")
+	sub := logger.With(slog.Bool("sub", true))
+	sub.Info("Hello from the sub logger", slog.String("subkey", "yes"))
 }
 
 func sleep() {

docs/img/prefix.gif

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"log/slog"
 	"math/rand/v2"
 	"net/http"
 	"os"
@@ -13,14 +14,26 @@ func main() {
 	logger := log.New(os.Stderr)
 	prefixed := logger.Prefixed("http")
 
-	logger.Info("Calling GitHub API", "url", "https://api.github.com/")
+	logger.Info("Calling GitHub API", slog.String("url", "https://api.github.com/"))
 	sleep()
 
-	prefixed.Warn("Slow endpoint", "endpoint", "users/slow", "duration", 10*time.Second)
+	prefixed.Warn(
+		"Slow endpoint",
+		slog.String("endpoint", "users/slow"),
+		slog.Duration("duration", 10*time.Second),
+	)
 	sleep()
-	prefixed.Info("Response from get repos", "status", http.StatusOK, "duration", 500*time.Millisecond)
+	prefixed.Info(
+		"Response from get repos",
+		slog.Int("status", http.StatusOK),
+		slog.Duration("duration", 500*time.Millisecond),
+	)
 	sleep()
-	prefixed.Error("Response from something else", "status", http.StatusBadRequest, "duration", 33*time.Millisecond)
+	prefixed.Error(
+		"Response from something else",
+		slog.Int("status", http.StatusBadRequest),
+		slog.Duration("duration", 33*time.Millisecond),
+	)
 }
 
 func sleep() {

examples/demo/main.go

@@ -29,7 +29,8 @@ const (
 	errorString = "ERROR"
 )
 
-func (l Level) styled() string {
+// String returns the stylised representation of the log level.
+func (l Level) String() string {
 	switch l {
 	case LevelDebug:
 		return debugStyle.Text(debugString)

examples/keys/main.go

@@ -11,8 +11,8 @@ package log // import "go.followtheprocess.codes/log"
 import (
 	"bytes"
 	"context"
-	"fmt"
 	"io"
+	"log/slog"
 	"os"
 	"slices"
 	"strconv"
@@ -37,9 +37,6 @@ const (
 	errorStyle     = hue.Red | hue.Bold
 )
 
-// missingValue is the placeholder text for a missing value in a log line's key value pair.
-const missingValue = "<MISSING>"
-
 // ctxKey is the unexported type used for context key so this key never collides with another.
 type ctxKey struct{}
 
@@ -54,7 +51,7 @@ type Logger struct {
 	mu         *sync.Mutex      // Protects w
 	timeFormat string           // The time format layout string, defaults to [time.RFC3339]
 	prefix     string           // Optional prefix to prepend to all log messages
-	kv         []any            // Persistent key value pairs
+	attrs      []slog.Attr      // Persistent key value pairs
 	level      Level            // The configured level of this logger, logs below this level are not shown
 	isDiscard  atomic.Bool      // w == [io.Discard], cached
 }
@@ -103,10 +100,10 @@ func FromContext(ctx context.Context) *Logger {
 // With returns a new [Logger] with the given persistent key value pairs.
 //
 // The returned logger is otherwise an exact clone of the caller.
-func (l *Logger) With(kv ...any) *Logger {
+func (l *Logger) With(attrs ...slog.Attr) *Logger {
 	sub := l.clone()
 
-	sub.kv = slices.Concat(sub.kv, kv)
+	sub.attrs = slices.Concat(sub.attrs, attrs)
 
 	return sub
 }
@@ -123,27 +120,27 @@ func (l *Logger) Prefixed(prefix string) *Logger {
 }
 
 // Debug writes a debug level log line.
-func (l *Logger) Debug(msg string, kv ...any) {
-	l.log(LevelDebug, msg, kv...)
+func (l *Logger) Debug(msg string, attrs ...slog.Attr) {
+	l.log(LevelDebug, msg, attrs...)
 }
 
 // Info writes an info level log line.
-func (l *Logger) Info(msg string, kv ...any) {
-	l.log(LevelInfo, msg, kv...)
+func (l *Logger) Info(msg string, attrs ...slog.Attr) {
+	l.log(LevelInfo, msg, attrs...)
 }
 
 // Warn writes a warning level log line.
-func (l *Logger) Warn(msg string, kv ...any) {
-	l.log(LevelWarn, msg, kv...)
+func (l *Logger) Warn(msg string, attrs ...slog.Attr) {
+	l.log(LevelWarn, msg, attrs...)
 }
 
 // Error writes an error level log line.
-func (l *Logger) Error(msg string, kv ...any) {
-	l.log(LevelError, msg, kv...)
+func (l *Logger) Error(msg string, attrs ...slog.Attr) {
+	l.log(LevelError, msg, attrs...)
 }
 
 // log logs the given levelled message.
-func (l *Logger) log(level Level, msg string, kv ...any) {
+func (l *Logger) log(level Level, msg string, attrs ...slog.Attr) {
 	if l.isDiscard.Load() || l.level > level {
 		// Do as little work as possible
 		return
@@ -157,7 +154,7 @@ func (l *Logger) log(level Level, msg string, kv ...any) {
 
 	buf.WriteString(timestampStyle.Text(l.timeFunc().Format(l.timeFormat)))
 	buf.WriteByte(' ')
-	buf.WriteString(level.styled())
+	buf.WriteString(level.String())
 
 	if l.prefix != "" {
 		buf.WriteString(" " + prefixStyle.Text(l.prefix))
@@ -173,24 +170,14 @@ func (l *Logger) log(level Level, msg string, kv ...any) {
 	buf.WriteString(strings.Repeat(" ", padding))
 	buf.WriteString(msg)
 
-	if numKVs := len(l.kv) + len(kv); numKVs != 0 {
-		kvs := make([]any, 0, numKVs)
-
-		kvs = append(kvs, l.kv...)
-		if len(kvs)%2 != 0 {
-			kvs = append(kvs, missingValue)
-		}
-
-		kvs = append(kvs, kv...)
-		if len(kvs)%2 != 0 {
-			kvs = append(kvs, missingValue)
-		}
+	if totalAttrs := len(l.attrs) + len(attrs); totalAttrs != 0 {
+		all := slices.Concat(l.attrs, attrs)
 
-		for i := 0; i < len(kvs); i += 2 {
+		for _, attr := range all {
 			buf.WriteByte(' ')
 
-			key := keyStyle.Sprint(kvs[i])
-			val := fmt.Sprintf("%+v", kvs[i+1])
+			key := keyStyle.Text(attr.Key)
+			val := attr.Value.String()
 
 			if needsQuotes(val) || val == "" {
 				val = strconv.Quote(val)