[API Proposal]: MemoryMarshal.CreateReadOnlySpan that takes in param

[benaadams]

Background and motivation

Currently CreateReadOnlySpan takes a ref so if a readonly field is passed it needs to first go via Unsafe.AsRef(in which seems an unnecessary friction of converting the type to non readonly.

API Proposal

namespace System.Runtime.InteropServices;

public static partial class MemoryMarshal
{
    public static ReadOnlySpan<T> CreateReadOnlySpan<T>(scoped in T reference, int length);
}

API Usage

// Fancy the value
readonly int _value;

MemoryMarshal.CreateReadOnlySpan(in _value, 1);

Alternative Designs

No response

Risks

No response

[ghost]

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Issue Details

---

Background and motivation

Currently CreateReadOnlySpan takes a ref so if a readonly field is passed it needs to first go via Unsafe.AsRef(in which seems an unnecessary friction of converting the type to non readonly.

API Proposal

namespace System.Runtime.InteropServices;

public static partial class MemoryMarshal
{
    public static ReadOnlySpan<T> CreateReadOnlySpan<T>(scoped in T reference, int length);
}

API Usage

// Fancy the value
readonly int _value;

MemoryMarshal.CreateReadOnlySpan(in _value, 1);

Alternative Designs

No response

Risks

No response

Author:	benaadams
Assignees:	-
Labels:	api-suggestion, area-System.Memory
Milestone:	-

[Sergio0694]

I think the plan is to change the existing API to take a ref readonly reference (see here), rather than adding a new API. One of the main reasons of ref readonly is specifically to allow changing the signature of existing API without breaking code. Also in technically would be incorrect as it would also allow rvalues, which shouldn't be used to create a span 🙂

[stephentoub]

Yup, what @Sergio0694 said. And even if we wanted to we couldn't add the proposed method; we can't overload based on ref vs in.

[tannergooding]

CC. @jaredpar since he's championing the issue.

Just an FYI that this is "another" case that would be switched from ref to ref readonly if possible.

[tannergooding]

Closing this as inactionable at the moment. We can revisit if the language adds support for ref readonly