Memory/ReadOnlyMemory cast/extensions (as Span)

[benaadams]

Parallel the Span<T> cast extensions for Memory<T>

e.g.

static Span<byte> AsBytes<T>(this Span<T> source) where T : struct
static ReadOnlySpan<byte> AsBytes<T>(this ReadOnlySpan<T> source) where T : struct
static Span<TTo> NonPortableCast<TFrom, TTo>(this Span<TFrom> source) where TFrom : struct where TTo : struct
static ReadOnlySpan<TTo> NonPortableCast<TFrom, TTo>(this ReadOnlySpan<TFrom> source) where TFrom : struct where TTo : struct

i.e

static Memory<byte> AsBytes<T>(this Memory<T> source) where T : struct
static ReadOnlyMemory<byte> AsBytes<T>(this ReadOnlyMemory<T> source) where T : struct
static Memory<TTo> NonPortableCast<TFrom, TTo>(this Memory<TFrom> source) where TFrom : struct where TTo : struct
static ReadOnlySpan<TTo> NonPortableCast<TFrom, TTo>(this ReadOnlyMemory<TFrom> source) where TFrom : struct where TTo : struct

/cc @KrzysztofCwalina @stephentoub @davidfowl

[KrzysztofCwalina]

I think AsBytes is fine. Do we need the NonPortableCast? Such an ugly name.

cc: @jkotas, @ahsonkhan

[benaadams]

To convert from Bytes to something else?

[stephentoub]

What does the implementation of AsBytes look like? e.g. if I construct a Memory<int> from an int[], and I then use AsBytes to get a Memory<byte>, what is the object stored in the Memory<byte>? What do I get out of its TryGetArray?

[benaadams]

What do I get out of its TryGetArray?

Would need to allocate an indirection OwnedMemory<T> to nullify the return 😢

So probably worse getting a Span from the Memory, converting the Span and copying to a pooled array and using that

[benaadams]

Yeah isn't going to work as can't put a reference of general "TFrom" in OwnedMemory<TTo> and get it to work