Nullable ref Value property

[emceelovin]

FEATURE_NAME

• Proposed
• Prototype: Not Started
• Implementation: Not Started
• Specification: Not Started

Summary

To avoid CS1612's, unnecessary copies, and because it just makes sense, Nullable.Value should be updated to return by reference.

Detailed design

public struct NestedValueType
{
    public string StringProp { get; set; }
}

public struct Nullable<T>
{
    // public ref T Value => ref _value
    public T Value => _value;

    public ref T ByRefValue => ref _value;

    T _value;
}

public void Serialize(ref Nullable<NestedValueType> obj)
{
    /*
     * CS1612. StringProperty is returned as a copy as it's the return value of the internal getter and not a variable.
     */
    obj.Value.StringProp = reader.ReadString();

    /*
     * Bingo. Zero copies of any of the value type's anywhere. The desirable should-be outcome. 
     */
    obj.ByRefValue.StringProp = string.Empty;

    /*
     * This shouldn't break anything
     * either. If you were to try and assign the ref read property to a non reference, it would just be copied like the typical
     * non by ref property
     */
    NestedValueType copy = obj.ByRefValue;
}

Drawbacks

You tell me?

Alternatives

// I emitted the IL version of this with DynamicMethod and ILGenerator
public ref T GetNullableValueByRef<T>(ref Nullable<T> nullable)
{
    return ref nullable._value;
}

[CyrusNajmabadi]

Moving to runtime. This is not a language decision.

[PathogenDavid]

Nullable.GetValueRefOrDefaultRef<T> has been accepted to .NET 7 and is already available in .NET 7 previews.

(See PR #64677 and API proposal #1534)

[emceelovin]

Thank you, David, and I figured I should've put this in runtime. All of that is great to hear!