Concise call keyword arg with default by conditional

[halleysfifthinc]

@taotree

Either I have to write a conditional at the call site, or have function A have both a default value for the argument (I need that for other cases) and convert a nothing value to that default value inside the function.

The latter is the idiomatic/Julian solution: assign kwarg=nothing in the signature, and in the function body, and set kwarg to its default value if isnothing(kwarg). nothing serves as an “unset” sentinel value that doesn’t special case a regular value (e.g. using -1 as the “unset” value). nothing could even still be used as a valid value by giving the kwarg as Some(nothing).

function A(x; kwarg=nothing)
    if isnothing(kwarg)
        kwarg = 100
    end
    # rest of function
end