Efficient broadcast comparison

[cstjean]

On 0.6,

julia> heys1 = fill("Hey", 10000);

julia> heys3 = CategoricalVector(heys1);

julia> @btime heys1 .== "Hey";
  62.509 μs (21 allocations: 6.19 KiB)

julia> @btime heys3 .== "Hey";
  101.900 μs (21 allocations: 6.19 KiB)

Theoretically the second comparison should be faster, since it should boil down to comparing integers (or, in this case, realizing that no value in the pool is ==). Is there a way of implementing this? I'm not familiar with broadcasting innards.

[nalimilan]

Yes, that would be a nice optimization. I'm not sure how hard it would be to override the broadcast machinery to implement this. One difficulty is that only the case where the second argument is a scalar can be handled efficiently, for more complex situations the generic fallback is OK.