@default

@default(expr) supplies the value a field takes when the author omits it. The expression is any constant value of the field's type.

Absent-equivalent defaults — an empty list, false, an empty string — are always safe to emit, since they behave the same as leaving the field out.

@block("server") type Server {
  @default(8080) port: u16
  @default([]) tags: list<utf8>
}

server web {}   // port = 8080, tags = []