.Struct: ClassType
.Struct.
    __call__: (format: Str) -> .Struct
    format: Str
    size: Nat
    pack: (self: .Struct, *values: Obj) -> Bytes
    unpack: (self: .Struct, bytes: Bytes) -> Obj

.pack: (format: Str, *values: Obj) -> Bytes
.unpack: (format: Str, bytes: Bytes) -> Obj
.calcsize: (format: Str) -> Nat