Transcoder = object
  stringToBuffer*: proc (s: string; vb: var VBuffer): bool {.nimcall, ...gcsafe,
      noSideEffect, ...raises: [Defect].}
  bufferToString*: proc (vb: var VBuffer; s: var string): bool {.nimcall,
      ...gcsafe, noSideEffect, ...raises: [Defect].}
  validateBuffer*: proc (vb: var VBuffer): bool {.nimcall, ...gcsafe, noSideEffect,
      ...raises: [Defect].}