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).