CODEWITHSUNDEEP
c#returnrefc#-7.0
ventiseis
ventiseis

Reputation: 3099

Why can't I ref return a static readonly field?

The following code doesn't compile with C# 7.0 / Visual Studio 2017.2:

class C {
    private static readonly int s = 5;
    public static ref int Data => ref s;
}

Is there an technical reason for disallowing references on static readonly fields or is this just a missing feature?

The error message says:

CS8162: A static readonly field cannot returned by reference.

Upvotes: 2

Views: 993

Answers (3)

Dmitry S.
Dmitry S.

Reputation: 8503

This is now possible in C# 7.2.

class C {
    private static readonly int s = 5;
    public static ref readonly int Data => ref s;
}

Upvotes: 4

David Arno
David Arno

Reputation: 43254

You can't yet return a reference to a readonly field, as ref returns are mutable. However, the ref readonly feature is planned for a future version of C# (currently pencilled in for C# 7.2, but that may change).

This feature will likely address both the ability to return references to readonly fields, as well as allowing ref parameters to be marked as readonly too, to offer the guarantee that the values referenced won't be modified by the method.

Upvotes: 3

SLaks
SLaks

Reputation: 887453

Because it's readonly.

The point of ref is to allow the referenced variable to be changed, which would violate readonly.

Upvotes: 10

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