How to skip arguments when using a function

General Usage
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9

Your second definition replaces the first (the names don’t matter, only the types so here in both cases you have “4 generic arguments”).

Here are some possibilities:

  1. Users can give nothing for JacobF:

    # method 1
FDEsolver(F, tSpan, y0, β, ::Nothing, par...)
# method 2
FDEsolver(F, tSpan, y0, β, JacobF, par...)

    then users can write FDEsolver(F, tSpan, y0, β, nothing, ...) to get the first method.

  2. Make the second method more specific by giving a type for JacobF, for example:

    # method 1
FDEsolver(F, tSpan, y0, β, par...)
# method 2
FDEsolver(F, tSpan, y0, β, JacobF::AbstractMatrix{<:Real}, par...)

    This works if the first par argument never has the same type as JacobF: then Julia can use the type of the 5th argument to decide which method to call.

  3. Get rid of the vararg. What are these parameters? maybe there’s a better way to pass them than using a vararg?

  4. Pass JacobF as an optional keyword argument:

    FDEsolver(F, tSpan, y0, β, par...; JacobF=nothing)

    Then in the definition of FDEsolver you can do if isnothing(JacobF) .... Or you can dispatch on its value like in option 1, but hidden from the user:

    # method 1 and 2
FDEsolver(F, tSpan, y0, β, par...; JacobF=nothing) = _FDEsolver(F, tSpan, y0, β, JacobF, par...)

# unexported methods
_FDEsolver(F, tSpan, y0, β, ::Nothing, par...) = ...
_FDEsolver(F, tSpan, y0, β, JacobF, par...) = ...
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