runtime: Passing default SequencePosition to ReadOnlySequence.Slice shouldn't throw NullRef

string jsonString = "a";

ReadOnlyMemory<byte> dataMemory = Text.Encoding.UTF8.GetBytes(jsonString);

var firstSegment = new BufferSegment<byte>(dataMemory.Slice(0, 1));
ReadOnlyMemory<byte> secondMem = dataMemory.Slice(0, 0);
BufferSegment<byte> secondSegment = firstSegment.Append(secondMem);

// A two segment sequence where the second one is empty: [a]-> []
var sequence = new ReadOnlySequence<byte>(firstSegment, 0, secondSegment, secondMem.Length);
sequence = sequence.Slice(default(SequencePosition));

System.NullReferenceException : Object reference not set to an instance of an object.
        Stack Trace:
          E:\GitHub\Fork\corefx\src\System.Memory\src\System\Buffers\ReadOnlySequence.Helpers.cs(243,0): at System.Buffers.ReadOnlySequence`1.BoundsCheck(SequencePosition& position)
          E:\GitHub\Fork\corefx\src\System.Memory\src\System\Buffers\ReadOnlySequence.cs(416,0): at System.Buffers.ReadOnlySequence`1.Slice(SequencePosition start)

cc @davidfowl, @pakrym

About this issue

Original URL
State: closed
Created 5 years ago
Comments: 16 (16 by maintainers)

Most upvoted comments

I think default(SequencePosition) should be “position 0”, and so: Slice(default, default) returns empty sequence Slice(default, x) returns sequence from beginning to x Slice(x, default) return empty if x == 0 and throws “end has to be after start” ix x > 0

KrzysztofCwalina on Mar 5, 2019

I think Slice on ros.Slice(0, default) should behave the same way as span.Slice(0, default) or memory.Slice(0, default) or s.Substring(0, default).

Assigning contextual meaning to default(SP) doesn’t feel right.

pakrym on Mar 5, 2019

@ahsonkhan I’m leaning towards treating default(Position) as “0” position.

So ros.Slice(default) would return the whole thing and ros.Slice(0, default) would return empty.

pakrym on Feb 28, 2019