Why isn't a byte slice a valid key? If anything, there should be a pretty straightforward equality check on an array of bytes.

A slice is not an array of bytes. That's exactly the point.

See http://blog.golang.org/go-slices-usage-and-internals to get a basic understanding

OK so I've read it. Slices sound exactly like one would guess, using the word from other languages. A view into an array.

So exactly why are they not suitable for equality? Even that article starts with "Slices are analogous to arrays in other languages". Please elaborate on this basic thing.

For an array (which are value types in go) you have the obvious element-wise equality.

For slices? Also element-wise? Even with different capacities? If the refer to the same window in the underlying array? Is there a need to copy the slice for inserting it to the map? Probably yes, because otherwise you could mutate the key from outside. But then it would be inconsistent to assignment (slices are reference types).

I have no idea how this could be done concisely.

Yes, element wise, why anything else? Different lengths are not equal; if capacity is externally visible, then that needs to be part of the compare.

As far as the whole ownership issue, that's a bit more than just ==, isn't it? Equality was the only thing I was questioning.

My thoughts exactly