tracer flags auto flag with std lib's pkg

Author: lainio

err2_init.go

@@ -0,0 +1,13 @@
+package err2
+
+import (
+	"flag"
+
+	"github.com/lainio/err2/internal/tracer"
+)
+
+func init() {
+	flag.Var(&tracer.Log, "err2-log", "stream for logging")
+	flag.Var(&tracer.Error, "err2-trace", "stream for error tracing")
+	flag.Var(&tracer.Panic, "err2-panic-trace", "stream for panic tracing")
+}

internal/tracer/tracer.go

@@ -5,6 +5,8 @@ import (
 	"io"
 	"os"
 	"sync/atomic"
+
+	"github.com/lainio/err2/internal/x"
 )
 
 type value struct {
@@ -37,3 +39,22 @@ func (v *value) Tracer() io.Writer {
 func (v *value) SetTracer(w io.Writer) {
 	v.Store(writer{w: w})
 }
+
+// String is part of the flag interfaces
+func (v *value) String() string {
+	return x.Whom(v.Tracer() != nil, "true", "false")
+}
+
+// Get is part of the flag interfaces, getter.
+func (v *value) Get() any { return nil }
+
+// Set is part of the flag.Value interface.
+func (v *value) Set(value string) error {
+	switch value {
+	case "stderr":
+		v.SetTracer(os.Stderr)
+	case "stdout":
+		v.SetTracer(os.Stdout)
+	}
+	return nil
+}