Implement std::io traits for IStream/ISequentialStream

[tim-weis]

Suggestion

The Read/Write/Seek traits in std::io form a battle-tested^{[citation needed]} abstraction over (de-)serializing implementations, that roughly map to these COM interfaces:

• IStream: Read/Write/Seek
• ISequentialStream: Read/Write

It would be convenient to have those implemented (I can supply a draft PR for discussion if desired).

Ignoring the maintenance burden, the only issue I see is how to deal with the impedance mismatch between the representation of sizes/offsets: std::io chooses [i|u]size (i.e., pointer precision), whereas the COM interfaces are based on [U]LARGE_INTEGER (64-bit quantities).

This could be addressed

• at compile-time (via conditional compilation), or
• run time (via Result<> or panic!())

[kennykerr]

Is this related to #1952?

[tim-weis]

Is this related to #1952?

Both issues have the same goal, so yes, they are related. Thanks for digging that up!

A few differences:

• This issue is asking for Read/Write/Seek as opposed to just Read
• IStream/ISequentialStream have a synchronous interface with the WinRT types offering an async interface only

If you're still planning on providing those std::io traits I would expect that implementing them for the COM interfaces is easier.