Why aref_calls, df_calls and h_calls all Vector{Int}?

[junyuan-chen]

It seems strange to me that these fields are Vector{Int} when the objective types (OnceDifferentiable etc.) are already mutable. Is there any use case where a vector is needed to hold multiple values? Would having these fields as Int be sufficient?

Also, the way to set/retrieve these counters are not explicitly made into the interface. But, there could be some functions defined just for that so that external packages do not have to hardcode the field names.

[pkofod]

I don't think it's necessary, no.