Documentation for field accessors is incorrect

[JakeSays]

Type of issue

Code doesn't work

Description

The document states that ref is optional for read-only field accessors. This appears to be incorrect, as an BadImageException is thrown with "Invalid usage of UnsafeAccessorAttribute" if ref is not specified.

This line in the documentation should be changed:
"The return value for an accessor to a field can be ref if setting of the field is desired."
to indicate that ref is always required for both read-only and read-write access.

Given this class:

public class Foo
{
    private string _field;
}

According to the documentation as written this is valid:

[UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_field")]
static extern string GetField(Foo foo);

When in fact it throws the above mentioned exception.
This code runs correctly:

[UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_field")]
static extern ref string GetField(Foo foo);

Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.unsafeaccessorattribute?view=net-9.0

Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Runtime.CompilerServices/UnsafeAccessorAttribute.xml

Document Version Independent Id

d8b3e8e8-a5e1-1884-99f2-678cf6a77a45

Platform Id

cbce44e6-89f0-7d37-b0fd-cb328dfbdd90

Article author

@dotnet-bot

[dotnet-issue-labeler]

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[dotnet-issue-labeler]

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[michaelgsharp]

Thanks for finding this. Based on the code comments you are 100% correct.

// The return type must be byref.
// If the non-static field access is for a
// value type, the instance must be byref.

[ericstj]

Appears to be addressed with #10268

[michaelgsharp]

Resolved by #10268