StringSegment GetHashCode() includes the Offset but Equals doesn't care about it

[IanMercer]

Surely GetHashCode() should not rely on the Offset since in Equals, two StringSegments are equal if they have equal values regardless as to where they are located in the string.

[pranavkm]

Yup, seems like a bug. It should probably add individual chars to the HashCodeCombiner to compute the hash.

[IanMercer]

I think if you just delete these two lines from GetHashCode it's all good:

        hash.Add(Offset);
        hash.Add(Length);

But yes, if you can do it without an allocation that might be better.

[pranavkm]

Wouldn't that still be problematic if the two strings are different but the StringSegments are identical.

[IanMercer]

Value is Buffer.Substring(Offset, Length)

So either you add Value to the Hashcode (which is effectively what Equals is looking at), or you add the characters from Buffer from position Offset for Length characters.

[pranavkm]

Huh. I thought it was adding the Buffer to the combiner. Allocating as part of GetHashCode seems counter to the purpose of this type. cc @rynowak.

[IanMercer]

Interestingly ArraySegment has different (and arguably rather useless) semantics for Equals: it does a compare on the whole buffer and the length and the offset. When would that ever be useful? Since StringSegment and ArraySegment are convenient ways of slicing strings and arrays to save copying you'd expect Equals to work like it would if you had copied the segment out, i.e. do the characters match (or do the array elements match).

[Eilon]

@pranavkm please confirm with @rynowak what the expectation is here.