[API Proposal]: Implement IAsyncDisposable on `TextReader`

[Neme12]

Background and motivation

By default, when disposing a StreamReader or StreamWriter, the underlying Stream itself is disposed. Since Stream supports async disposal via IAsyncDisposable, both StreamReader and StreamWriter should implement IAsyncDisposable as well to support the case when the underlying stream supports it. Currently, only StreamWriter implements IAsyncDisposable while StreamReader doesn't, so when using StreamReader, it's only possible to dispose the underlying stream synchronously.

API Proposal

namespace System.IO;

// new
public abstract partial class TextReader : MarshalByRefObject, IDisposable, IAsyncDisposable
{
    public virtual ValueTask DisposeAsync();
}

// existing
public abstract partial class TextWriter : MarshalByRefObject, IDisposable, IAsyncDisposable
{
    public virtual ValueTask DisposeAsync();
}

// new
public partial class StreamReader : TextReader
{
    public override ValueTask DisposeAsync();
}

// existing
public partial class StreamWriter : TextWriter
{
    public override ValueTask DisposeAsync();
}

API Usage

await using var reader = new StreamReader(myAsyncStream);

Alternative Designs

No response

Risks

No response

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Issue Details

---

Background and motivation

By default, when disposing a StreamReader or StreamWriter, the underlying Stream itself is disposed. Since Stream supports async disposal via IAsyncDisposable, both StreamReader and StreamWriter should implement IAsyncDisposable as well to support the case when the underlying stream supports it. Currently, only StreamWriter implements IAsyncDisposable while StreamReader doesn't, so when using StreamReader, it's only possible to dispose the underlying stream synchronously.

API Proposal

namespace System.IO;

// new
public abstract partial class TextReader : MarshalByRefObject, IDisposable, IAsyncDisposable
{
    public virtual ValueTask DisposeAsync();
}

// existing
public abstract partial class TextWriter : MarshalByRefObject, IDisposable, IAsyncDisposable
{
    public virtual ValueTask DisposeAsync();
}

// new
public partial class StreamReader : TextReader
{
    public override ValueTask DisposeAsync();
}

// existing
public partial class StreamWriter : TextWriter
{
    public override ValueTask DisposeAsync();
}

API Usage

await using var reader = new StreamReader(myAsyncStream);

Alternative Designs

No response

Risks

No response

Author:	Neme12
Assignees:	-
Labels:	api-suggestion, area-System.IO
Milestone:	-

[adamsitnik]

Hi @Neme12

Thank you for your proposal. It sounds very reasonable to me, so I've marked it as ready for review. It should get reviewed by our API Review Board within few weeks.

[terrajobst]

Video

• Looks good as proposed

namespace System.IO;

public partial class TextReader
{
    public virtual ValueTask DisposeAsync();
}

public partial class StreamReader : TextReader
{
    public override ValueTask DisposeAsync();
}