Understanding issorted's lt keyword

New to Julia
68

That is not correct. All you need is < / isless. Take for example

julia> mutable struct Wrap
       _::Int
       end

julia> Base.isless(a::Wrap, b::Wrap) = isless(a._, b._)

julia> Wrap(3) == Wrap(3)
false

julia> issorted(map(Wrap, 1:10))
true

julia> issorted(map(Wrap, [1, 1, 1]))
true