C# Access private property backing field using Unsafe Accessor

One less-known feature of the UnsafeAccessorAttribute is that it also allows you to access auto-generated backing fields of auto-properties – fields with unspeakable names.

The way to access them is very similar to accessing fields, the only difference being the member name pattern, which looks like this:

<MyProperty>k__BackingField

Let’s take the following class as an example:

class Foo
{
    private string InstanceProperty { get; set; } = "instance-property";
}

Below you have the unsafe accessor for the backing field of this property and examples on how to read the private backing field and how to modify its value.

[UnsafeAccessor(UnsafeAccessorKind.Field, Name = "<InstanceProperty>k__BackingField")]
extern static ref string InstancePropertyBackingField(Foo @this);

var instance = new Foo();

// Read
_ = InstancePropertyBackingField(instance);

// Modify
InstancePropertyBackingField(instance) = Guid.NewGuid().ToString();