Often you have an array and you just want to use it. With the current
design, you have to first construct a `BinaryByteStream`, and then create
a `BinaryStreamRef` from it. Worse, the `BinaryStreamRef` holds a pointer
to the `BinaryByteStream`, so you can't just create a temporary one to
appease the compiler, you have to actually hold onto both the `ArrayRef`
as well as the `BinaryByteStream` *AND* the `BinaryStreamReader` on top of
that. This makes for very cumbersome code, often requiring one to store a
`BinaryByteStream` in a class just to circumvent this.
At the cost of some added complexity (not exposed to users, but internal
to the library), we can do better than this. This patch allows us to
construct `BinaryStreamReaders` and `BinaryStreamWriters` directly from
source data (e.g. `StringRef`, `MutableArrayRef<uint8_t>`, etc). Not only
does this reduce the amount of code you have to type and make it more
obvious how to use it, but it solves real lifetime issues when it's
inconvenient to hold onto a `BinaryByteStream` for a long time.
The additional complexity is in the form of an added layer of indirection.
Whereas before we simply stored a `BinaryStream*` in the ref, we now store
both a `BinaryStream*` **and** a `std::shared_ptr<BinaryStream>`. When
the user wants to construct a `BinaryStreamRef` directly from an
`ArrayRef` etc, we allocate an internal object that holds ownership over a
`BinaryByteStream` and forwards all calls, and store this in the
`shared_ptr<>`. This also maintains the ref semantics, as you can copy it
by value and references refer to the same underlying stream -- the one
being held in the object stored in the `shared_ptr`.
Differential Revision: https://reviews.llvm.org/D33293
llvm-svn: 303294
Zachary Turner