Remiplement Add to use reflection.

Now it matters whether `FieldLabel`s are spelled correctly, but in return, we don't have to write and maintain that obnoxious `switch` statement.

koboldsim/cardtypes.go

@@ -9,7 +9,6 @@ import (
 var (
 	ErrOptionNotEnabled = errors.New("option not enabled")
 	ErrPolicyNotEnacted = errors.New("cannot unenact policy that is not enacted")
-	ErrNoFieldLabel     = errors.New("field does not exist")
 
 	// ErrUnimplemented and ErrKeepMessaage are "non-errors". They are used
 	// as special signals that the result needs to be handled in a special way;

koboldsim/stats.go

@@ -1,7 +1,9 @@
 package koboldsim
 
 import (
+	"errors"
 	"fmt"
+	"reflect"
 
 	"git.chromaticdragon.app/kistaro/CardSimEngine/cardsim"
 )
@@ -167,6 +169,10 @@ func NewKoboldMine() *KoboldMine {
 	}
 }
 
+// FieldLabel instances are strings exactly matching the name of an
+// exported field in `KoboldMine`. These are used to map field names to
+// amounts to change in `TablePolicy` instances, which are then looked
+// up by name (via reflection) when adding the stat.
 type FieldLabel string
 
 const (
@@ -188,56 +194,51 @@ const (
 	Secrecy          FieldLabel = "Secrecy"
 )
 
-func (k *KoboldMine) Add(which FieldLabel, amount float64) error {
-	switch which {
-	case Authoritarianism:
-		k.Authoritarianism += amount
-		return nil
-	case BasePopulation:
-		k.BasePopulation += amount
-		return nil
-	case Bureaucracy:
-		k.Bureaucracy += amount
-		return nil
-	case Construction:
-		k.Construction += amount
-		return nil
-	case Cruelty:
-		k.Cruelty += amount
-		return nil
-	case Education:
-		k.Education += amount
-		return nil
-	case FoodSupply:
-		k.FoodSupply += amount
-		return nil
-	case ForeignRelations:
-		k.ForeignRelations += amount
-		return nil
-	case Gullibility:
-		k.Gullibility += amount
-		return nil
-	case Madness:
-		k.Madness += amount
-		return nil
-	case Manufacturing:
-		k.Manufacturing += amount
-		return nil
-	case Mining:
-		k.Mining += amount
-		return nil
-	case Militarism:
-		k.Militarism += amount
-		return nil
-	case Rebellion:
-		k.Rebellion += amount
-		return nil
-	case Scavenging:
-		k.Scavenging += amount
-		return nil
-	case Secrecy:
-		k.Secrecy += amount
+// ErrBadFieldLabel is an "error category" for all errors where a
+// FieldLabel did not correctly name a Field that could be used in Add.
+var ErrBadFieldLabel = errors.New("bad field label")
+
+// ErrNoFieldLabel is a kind of `ErrBadFieldLabel` used when no field
+// of the target has the exact name specified in the FieldLabel. Check
+// spelling and capitalization.
+var ErrNoFieldLabel = fmt.Errorf("%w: field does not exist", ErrBadFieldLabel)
+
+// ErrFieldNotFloat is a kind of `ErrBadFieldLabel` used when it is not
+// possible to read and assign a float to the named field. Is this the
+// name of a calculated stat (a function) rather than a base stat?
+var ErrFieldNotFloat = fmt.Errorf("%w: field type is not float", ErrBadFieldLabel)
+
+// ErrFieldSetPanic is a kind of `ErrBadFieldLabel` used when trying to
+// set the value of a field panicked. The panic message should be
+// preserved in the error to diagnose the problem. If the problem is
+// that the field is unexported, capitalize the name (including inside
+// the KoboldMine type). Any other issue is a more complicated bug,
+// because all of them that aren't already caught by ErrFieldNotFloat
+// imply something very unexpected happened with `k` itself (in `Add`).
+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) {
+	kv := reflect.ValueOf(k).Elem()
+	f := kv.FieldByName(string(which))
+	if !f.IsValid() {
+		return fmt.Errorf("cannot add %f to field %q: %w", amount, which, ErrNoFieldLabel)
+	}
+	if !f.CanFloat() {
+		return fmt.Errorf("cannot add %f to field %q: %w", amount, which, ErrFieldNotFloat)
+	}
+
+	defer func() {
+		if r := recover(); r != nil {
+			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
 }
-	return fmt.Errorf("cannot add %f to %q: %w", amount, which, ErrNoFieldLabel)
-}