Surprising runtime behaviour when wrapping functions

General Usage Performance
3

Thank you very much for your excellent answer. FYI, I was orienting towards NLSolversBase.jl

mutable struct OnceDifferentiable{TF, TDF, TX} <: AbstractObjective
    f # objective
    df # (partial) derivative of objective
    fdf # objective and (partial) derivative of objective
    F::TF # cache for f output
    DF::TDF # cache for df output
    x_f::TX # x used to evaluate f (stored in F)
    x_df::TX # x used to evaluate df (stored in DF)
    f_calls::Vector{Int}
    df_calls::Vector{Int}
end

which doesn’t even annotate the functions.