Constructor with Varargs

General Usage
1

This works

using Pipe, Parameters

@with_kw struct X
    A
    B
end

x = (A=1, B=2 )
X( x... )

but this fails

x = (A=1, B=2, C=3 )
X( x... )

unless you manually filter x to only contain the fields of X.
or manually create a varargs constructor X(; A, B, varargs... ) = X( A, B)

Is there a way around this ?
Can the X struct automatically create a constructor with Varargs… functionality.
So that unused variables are dropped without causing an error

2

You could create your own macro to do this.

Here is what that macro looks like when expanded.

julia> @macroexpand @with_kw struct X
           A
           B
       end
quote
    begin
        $(Expr(:meta, :doc))
        struct X
            A
            B
            X(; A = error("Field '" * "A" * "' has no default, supply it with keyword."), B = error("Field '" * "B" * "' has no default, supply it with keyword.")) = begin
                    X(A, B)
                end
            X(A, B) = begin
                    new(A, B)
                end
        end
    end
...
end
2 Likes
3

Thanks Mark. looks good.

I was hoping there would be a way for it to happen automatically. But doesn’t seem to be the case