What is Varargs optional and Keyword argument in Julia

This recipe explains what is Varargs optional and Keyword argument

Recipe Objective

This recipe explains what are varargs functions, optional arguments, and keyword arguments in julia.

Varargs Functions

Varargs stands for variable number of arguments. We use varargs function to write functions taking an arbitrary number of arguments.

bar(l,m,n...) = (l,m,n)
bar(4,5)
bar(4,5,6)
bar(4,5,6,7,8)
x = [4,5,6,7]
bar(x...)

Optional Arguments

We provide default values for function arguments in order to save time from having to pass every argument on every call.

function date(Year::Int64, Month::Int64=1, Date::Int64=1)
    f = validargs(date, Year, Month, Date)
    f === nothing || throw(f)
    return date(UTD(totaldays(Year, Month, Date)))
end

Keyword Arguments

Sometimes there are a large number of arguments in a function and remembering how to call this function is a bit tricky. Keyword arguments solve this problem by allowing arguments to be identified by name instead of only by position.

function func(a, b; style="solid", width=1, colour="blue")
    ###
end

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