just stumbled upon julia’s keyword mechanism
julia> func(a; b::B) where B = a func (generic function with 1 method) julia> func(1) ERROR: UndefKeywordError: keyword argument b not assigned Stacktrace:  func(::Int64) at .\none:1  top-level scope at none:0
To me it seems like it would make more sense to let
b undefined until either
B is accessed.
There already is
isundefined method which could be used to check this.