simplify, and 1.0

src/UniqueVectors.jl

@@ -167,14 +167,9 @@ function swap!(uv::UniqueVector, to::Int, from::Int)
 end
 
 function permute!(uv::UniqueVector, perm::AbstractVector)
-    # This allocates, but usually permute!(a, p) = permute!!(a, copymutable(p)) would anyway
     ip = invperm(perm)
     map!(i -> get(ip, i, 0), uv.lookup.vals, uv.lookup.vals)
-    if ismutable(ip)
-        Base.invpermute!!(uv.items, ip)  # save the allocation, so long as ip isn't an SVector or something
-    else
-        permute!(uv.items, perm)
-    end
+    permute!(uv.items, perm)
     return uv
 end