# Constructor with Varargs
**URL:** https://discourse.julialang.org/t/constructor-with-varargs/84568
**Category:** General Usage
**Tags:** parametersjl
**Created:** [July 21, 2022, 1:56am UTC](https://discourse.julialang.org/t/constructor-with-varargs/84568 "2022-07-21T01:56:26Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Lincoln\_Hannah](https://discourse.julialang.org/u/Lincoln_Hannah)
#### Post date: [July 21, 2022, 1:56am UTC](https://discourse.julialang.org/t/constructor-with-varargs/84568/1 "2022-07-21T01:56:26Z")
This works
```julia
using Pipe, Parameters
@with_kw struct X
A
B
end
x = (A=1, B=2 )
X( x... )
```
but this fails
```julia
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
---
### Author:  [@mkitti](https://discourse.julialang.org/u/mkitti)
#### Post date: [July 21, 2022, 2:21am UTC](https://discourse.julialang.org/t/constructor-with-varargs/84568/2 "2022-07-21T02:21:23Z")
You could create your own macro to do this.
Here is what that macro looks like when expanded.
```julia
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
```
---
### Author:  [@Lincoln\_Hannah](https://discourse.julialang.org/u/Lincoln_Hannah)
#### Post date: [July 21, 2022, 12:09pm UTC](https://discourse.julialang.org/t/constructor-with-varargs/84568/3 "2022-07-21T12:09:15Z")
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