StreamReader constructor documentation mismatch with implementation

[rameel]

There is an inconsistency between the documentation and the actual implementation of the StreamReader constructors. The documentation states that passing null to the Encoding parameter in some constructors, except the main one, will result in an exception being thrown. However, all these constructors pass the Encoding argument to the main constructor, which allows null.

public StreamReader(Stream stream, Encoding encoding);
public StreamReader(Stream stream, Encoding encoding, bool detectEncodingFromByteOrderMarks);
public StreamReader(Stream stream, Encoding encoding, bool detectEncodingFromByteOrderMarks, int bufferSize);

public StreamReader(Stream stream, Encoding? encoding = null, bool detectEncodingFromByteOrderMarks = true, int bufferSize = -1, bool leaveOpen = false)

StreamReader.cs
Documentation

Suggested Fix:

• Mark the Encoding parameter as nullable in these constructors.
• Update the documentation.

- public StreamReader(Stream stream, Encoding encoding);
- public StreamReader(Stream stream, Encoding encoding, bool detectEncodingFromByteOrderMarks);
- public StreamReader(Stream stream, Encoding encoding, bool detectEncodingFromByteOrderMarks, int bufferSize);
+ public StreamReader(Stream stream, Encoding? encoding);
+ public StreamReader(Stream stream, Encoding? encoding, bool detectEncodingFromByteOrderMarks);
+ public StreamReader(Stream stream, Encoding? encoding, bool detectEncodingFromByteOrderMarks, int bufferSize);

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-text-encoding
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

[jozkee]

Related to #106237.

[eriawan]

@jozkee
Could I take this issue to fix and assign this to me? This seems quite straightforward.

A PR will be up tomorrow 🙂

[rameel]

For reference, see #106658

[bartonjs]

Video

Keeping the behavior in .NET 10 but correcting the nullability annotations seems correct. Since .NET Framework does have those Encoding inputs as null-rejecting, the documentation probably needs to call that out as a version differentiated behavior.

- public StreamReader(Stream stream, Encoding encoding);
- public StreamReader(Stream stream, Encoding encoding, bool detectEncodingFromByteOrderMarks);
- public StreamReader(Stream stream, Encoding encoding, bool detectEncodingFromByteOrderMarks, int bufferSize);
+ public StreamReader(Stream stream, Encoding? encoding);
+ public StreamReader(Stream stream, Encoding? encoding, bool detectEncodingFromByteOrderMarks);
+ public StreamReader(Stream stream, Encoding? encoding, bool detectEncodingFromByteOrderMarks, int bufferSize);