uri_template_parse_error.pony

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class val URITemplateParseError
  """
  Describes why a URI template string failed to parse.

  Contains a human-readable error message and the byte offset in the
  template string where the error was detected.
  """
  let message: String val
  let offset: USize

  new val create(message': String val, offset': USize) =>
    """
    Create a parse error with the given message and byte offset.
    """
    message = message'
    offset = offset'

  fun string(): String =>
    """
    Format as "offset N: message".
    """
    recover val
      let num = offset.string()
      String(7 + num.size() + 2 + message.size())
        .> append("offset ")
        .> append(num)
        .> append(": ")
        .> append(message)
    end