Documentation of `ReadOnlyMemory<T>.Equals(ReadOnlyMemory<T>)` is technically ambiguous

[mfrischknecht]

Type of issue

Misleading wording.

Description

Two ReadOnlyMemory objects are equal if the memory regions point to the same array and have the same length. The method does not check to see if the contents are equal.

The wording here sounds like the ReadOnlyMemory<T> only compares _object and _length ¹ internally, ignoring the actual offset of the slice. The implementation seems to do the sensible thing ² and return true iff both instances point to the same memory region, however (at least on a naive read-through; I'm not sure about the possible edge cases the internal constructor ³ might introduce).

Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.readonlymemory-1.equals?view=net-10.0#system-readonlymemory-1-equals(system-readonlymemory((-0)))

Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System/ReadOnlyMemory`1.xml

Document Version Independent Id

c8fe03ad-b230-bf63-cd15-c862faa1eb22

Platform Id

ef16dd22-d568-3bdd-b282-372e16488fd6

Article author

@dotnet-bot

Footnotes

1. https://github.com/dotnet/runtime/blob/a962f34b0d502d551534bec84493edee67783771/src/libraries/System.Private.CoreLib/src/System/ReadOnlyMemory.cs#L26 ↩

2. https://github.com/dotnet/runtime/blob/a962f34b0d502d551534bec84493edee67783771/src/libraries/System.Private.CoreLib/src/System/ReadOnlyMemory.cs#L383 ↩

3. https://github.com/dotnet/runtime/blob/a962f34b0d502d551534bec84493edee67783771/src/libraries/System.Private.CoreLib/src/System/ReadOnlyMemory.cs#L93 ↩

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[tannergooding]

Contributions are welcome. The implementation does indeed check all three of _object, _index, and _length. Which means that two things pointing to the same memory, but via different mechanisms (such as one to the managed array and one via a pinned pointer) will not compare as equal.

That is, as far as memory is concerned the "array" includes the start index and so array.AsMemory(0, 5) and array.AsMemory(1, 5) are not equal, because they are "different arrays".