pull try out of Add

deferring a recovery handler is normal in Go but opaque. Pulling out a helper for this (`try`) makes it more obvious that this is just another "if this operation fails, return error" case.

koboldsim/stats.go

@@ -220,7 +220,7 @@ var ErrFieldSetPanic = fmt.Errorf("%w: panic when setting", ErrBadFieldLabel)
 // Use a FieldLabel to add an amount to the matching field. If no such
 // field can be found, the field is not exported, or the field is not
 // of type float64, this returns an error ad does not change any values.
-func (k *KoboldMine) Add(which FieldLabel, amount float64) (finalErr error) {
+func (k *KoboldMine) Add(which FieldLabel, amount float64) error {
 	kv := reflect.ValueOf(k).Elem()
 	f := kv.FieldByName(string(which))
 	if !f.IsValid() {
@@ -230,15 +230,8 @@ func (k *KoboldMine) Add(which FieldLabel, amount float64) (finalErr error) {
 		return fmt.Errorf("cannot add %f to field %q: %w", amount, which, ErrFieldNotFloat)
 	}
 
-	defer func() {
+	if err := try(func() { f.SetFloat(f.Float() + amount) }); err != nil {
-		if r := recover(); r != nil {
+		return fmt.Errorf("could not add %f to field %q: %w", amount, which, err)
-			if e, ok := r.(error); ok {
+	}
-				finalErr = fmt.Errorf("could not add %f to field %q: %w: %w", amount, which, ErrFieldSetPanic, e)
-			} else {
-				finalErr = fmt.Errorf("could not add %f to field %q: %w: %v", amount, which, ErrFieldSetPanic, r)
-			}
-		}
-	}()
-	f.SetFloat(f.Float() + amount)
 	return nil
 }

koboldsim/util.go

@@ -1,6 +1,8 @@
 package koboldsim
 
 import (
+	"errors"
+	"fmt"
 	"math"
 
 	"golang.org/x/exp/constraints"
@@ -47,3 +49,23 @@ func clamp[T constraints.Ordered](a, b, c T) T {
 	// `a` is neither most nor least; therefore, `a` is mid
 	return a
 }
+
+var ErrWrappedPanic = errors.New("panic")
+
+// try catches a panic in the provided func and demotes it to an error, if any
+// panic occurs. The returned error, if any, wraps `ErrWrappedPanic`. If the
+// panic argument is itself an error, it is also wrapped; otherwise, it is
+// stringified into the error message using `%v`.
+func try(f func()) (finalErr error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if e, ok := r.(error); ok {
+				finalErr = fmt.Errorf("%w: %w", ErrWrappedPanic, e)
+				return
+			}
+			finalErr = fmt.Errorf("%w: %v", ErrWrappedPanic, r)
+		}
+	}()
+	f()
+	return nil
+}