feat: decode arrays into [N]T and add MarshalAppend

Assisted-by: GLM 5.3 Flash

decode.go

@@ -309,31 +309,58 @@ func (d *decoder) assignMap(tbl map[string]any, dst reflect.Value) error {
 }
 
 func (d *decoder) assignSlice(items []any, dst reflect.Value) error {
-	if dst.Kind() != reflect.Slice {
+	switch dst.Kind() {
+	case reflect.Slice:
+		out := reflect.MakeSlice(dst.Type(), len(items), len(items))
+		for i, item := range items {
+			if err := d.assign(item, out.Index(i)); err != nil {
+				return newDecodeError(fmt.Sprintf("[%d]", i), err)
+			}
+		}
+		dst.Set(out)
+		return nil
+	case reflect.Array:
+		// A fixed-size array takes the elements in place; a length mismatch is
+		// the error, because a TOML array carries no way to name a default for
+		// the elements it is short of, and the surplus has nowhere to go.
+		if dst.Len() != len(items) {
+			return fmt.Errorf("interpres: cannot assign %d elements to %s", len(items), dst.Type())
+		}
+		for i, item := range items {
+			if err := d.assign(item, dst.Index(i)); err != nil {
+				return newDecodeError(fmt.Sprintf("[%d]", i), err)
+			}
+		}
+		return nil
+	default:
 		return fmt.Errorf("interpres: cannot assign array to %s", dst.Type())
 	}
-	out := reflect.MakeSlice(dst.Type(), len(items), len(items))
-	for i, item := range items {
-		if err := d.assign(item, out.Index(i)); err != nil {
-			return newDecodeError(fmt.Sprintf("[%d]", i), err)
-		}
-	}
-	dst.Set(out)
-	return nil
 }
 
 func (d *decoder) assignTableSlice(items []map[string]any, dst reflect.Value) error {
-	if dst.Kind() != reflect.Slice {
+	switch dst.Kind() {
+	case reflect.Slice:
+		out := reflect.MakeSlice(dst.Type(), len(items), len(items))
+		for i, item := range items {
+			if err := d.assign(item, out.Index(i)); err != nil {
+				return newDecodeError(fmt.Sprintf("[%d]", i), err)
+			}
+		}
+		dst.Set(out)
+		return nil
+	case reflect.Array:
+		if dst.Len() != len(items) {
+			return fmt.Errorf("interpres: cannot assign %d elements to %s", len(items), dst.Type())
+		}
+		for i, item := range items {
+			if err := d.assign(item, dst.Index(i)); err != nil {
+				return newDecodeError(fmt.Sprintf("[%d]", i), err)
+			}
+		}
+		return nil
+	default:
 		return fmt.Errorf("interpres: cannot assign array of tables to %s", dst.Type())
 	}
-	out := reflect.MakeSlice(dst.Type(), len(items), len(items))
-	for i, item := range items {
-		if err := d.assign(item, out.Index(i)); err != nil {
-			return newDecodeError(fmt.Sprintf("[%d]", i), err)
-		}
-	}
-	dst.Set(out)
-	return nil
 }
 
 // --- low-level setters -----------------------------------------------------