Compile-time reflection

Having built-in JSON support is nice, but V also allows you to create efficient serializers for any data format. V has compile-time if and for constructs:

  1. // TODO: not fully implemented
  3. struct User {
  4.     name string
  5.     age  int
  6. }
  8. // Note: T should be passed a struct name only
  9. fn decode<T>(data string) T {
  10.     mut result := T{}
  11.     // compile-time `for` loop
  12.     // T.fields gives an array of a field metadata type
  13.     $for field in T.fields {
  14.         $if field.typ is string {
  15.             // $(string_expr) produces an identifier
  16.             result.$(field.name) = get_string(data, field.name)
  17.         } $else $if field.typ is int {
  18.             result.$(field.name) = get_int(data, field.name)
  19.         }
  20.     }
  21.     return result
  22. }
  24. // `decode<User>` generates:
  25. fn decode_User(data string) User {
  26.     mut result := User{}
  27.     result.name = get_string(data, 'name')
  28.     result.age = get_int(data, 'age')
  29.     return result
  30. }