/// <summary>
/// Get an array segment from the underlying memory.
/// If unable to get the array segment, return false with a default array segment.
/// </summary>
public static bool TryGetArray <T>(ReadOnlyMemory <T> memory, out ArraySegment <T> segment)
{
object?obj = memory.GetObjectStartLength(out int index, out int length);
// As an optimization, we skip the "is string?" check below if typeof(T) is not char,
// as Memory<T> / ROM<T> can't possibly contain a string instance in this case.
if (obj != null && !(
(typeof(T) == typeof(char) && obj.GetType() == typeof(string))
#if FEATURE_UTF8STRING
|| ((typeof(T) == typeof(byte) || typeof(T) == typeof(Char8)) && obj.GetType() == typeof(Utf8String))
#endif // FEATURE_UTF8STRING
))
{
if (RuntimeHelpers.ObjectHasComponentSize(obj))
{
// The object has a component size, which means it's variable-length, but we already
// checked above that it's not a string. The only remaining option is that it's a T[]
// or a U[] which is blittable to a T[] (e.g., int[] and uint[]).
// The array may be prepinned, so remove the high bit from the start index in the line below.
// The ArraySegment<T> ctor will perform bounds checking on index & length.
segment = new ArraySegment <T>(Unsafe.As <T[]>(obj), index & ReadOnlyMemory <T> .RemoveFlagsBitMask, length);
return(true);
}
else
{
// The object isn't null, and it's not variable-length, so the only remaining option
// is MemoryManager<T>. The ArraySegment<T> ctor will perform bounds checking on index & length.
Debug.Assert(obj is MemoryManager <T>);
if (Unsafe.As <MemoryManager <T> >(obj).TryGetArray(out ArraySegment <T> tempArraySegment))
{
segment = new ArraySegment <T>(tempArraySegment.Array !, tempArraySegment.Offset + index, length);
return(true);
}
}
}
// If we got to this point, the object is null, or it's a string, or it's a MemoryManager<T>
// which isn't backed by an array. We'll quickly homogenize all zero-length Memory<T> instances
// to an empty array for the purposes of reporting back to our caller.
if (length == 0)
{
segment = ArraySegment <T> .Empty;
return(true);
}
// Otherwise, there's *some* data, but it's not convertible to T[].
segment = default;
return(false);
}