A `Bytes` type that can be an owned `List` or used with a `Buffer`

bytes_ref_or_owned.mojo

from buffer import Buffer
from utils.variant import Variant
from collections.list import List


@value
struct Bytes[mutability: __mlir_type.i1, lifetime: AnyLifetime[mutability].type](Sized):
    alias Variant = Variant[List[Int8], Buffer[DType.int8]]
    var variant: Self.Variant

    fn __len__(self) -> Int:
        if self.variant.isa[List[Int8]]():
            return len(self.variant.get[List[Int8]]()[])
        else:
            return len(self.variant.get[Buffer[DType.int8]]()[])

    fn __getitem__(self, index: Int) -> Int8:
        if self.variant.isa[String]():
            return self.variant.get[List[Int8]]()[][index]
        else:
            return self.variant.get[Buffer[DType.int8]]()[][index]

    fn __setitem__(inout self, index: Int, value: Int8):
        if self.variant.isa[String]():
            self.variant.get[List[Int8]]()[][index] = value
        else:
            self.variant.get[Buffer[DType.int8]]()[][index] = value


fn main():
    var input = String("Abcdefghijklmnop").as_bytes()
    var buf = Buffer[DType.int8](
        DTypePointer[DType.int8](input.data.bitcast[Int8]().value),
        len(input),
    )
    var bytes = Bytes[__mlir_attr.`1: i1`, __lifetime_of(input)](buf)
    for i in range(len(bytes)):
        print(chr(bytes[i].to_int()), end="")
    print()
    bytes[0] = ord("a")
    for i in range(len(bytes)):
        print(chr(bytes[i].to_int()), end="")
    print()
    bytes = Bytes[__mlir_attr.`1: i1`, __lifetime_of(input)](input)
    for i in range(len(bytes)):
        print(chr(bytes[i].to_int()), end="")
    print()
    bytes[0] = ord("a")
    for i in range(len(bytes)):
        print(chr(bytes[i].to_int()), end="")
    print()