add data command and utility functions for type assertion and map key access

util/must.go

@@ -1,5 +1,7 @@
 package util
 
+import "fmt"
+
 func MustOk[T any](v T, ok bool) T {
 	if !ok {
 		panic("not ok")
@@ -19,3 +21,20 @@ func Must(err error) {
 		panic(err)
 	}
 }
+
+func AssertTypeError[T any](v any) (T, error) {
+	var zero T
+	r, ok := v.(T)
+	if !ok {
+		return zero, fmt.Errorf("type assertion failed: %T cannot be asserted to %T", v, zero)
+	}
+	return r, nil
+}
+
+func MapGetError[K comparable, V any, M map[K]V](m M, k K) (V, error) {
+	v, ok := m[k]
+	if !ok {
+		return v, fmt.Errorf("key %v not found", k)
+	}
+	return v, nil
+}