# Automatic keyword argument constructor
**URL:** https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573
**Category:** General Usage
**Created:** [March 26, 2020, 10:58pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573 "2020-03-26T22:58:24Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@HugoTrentesaux](https://discourse.julialang.org/u/HugoTrentesaux)
#### Post date: [March 26, 2020, 10:58pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/1 "2020-03-26T22:58:24Z")
Is there a way to have Julia automatically defining a constructor using keywords arguments?
```julia
# the composite type
struct Person
name::String
age::Int
end
# generates automatically this constructor:
me = Person("Hugo", 24)
# is there a way to define automatically
# this constructor using only keyword arguments
# corresponding to fields names?
me = Person(;name="Hugo", age=24)
```
I think this could be achieved using macros, but I’m not good at it and do not know how to do. Now, I’m forced to implement it manually:
```julia
struct Person
name::String
age::Int
Person(;name::String,age::Int) = new(name,age)
end
```
It’s a bit cumbersome.
---
### Author:  [@Pbellive](https://discourse.julialang.org/u/Pbellive)
#### Post date: [March 26, 2020, 11:00pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/2 "2020-03-26T23:00:05Z")
I believe [Parameters.jl](https://github.com/mauro3/Parameters.jl) is exactly what you’re looking for
---
### Author:  [@HugoTrentesaux](https://discourse.julialang.org/u/HugoTrentesaux)
#### Post date: [March 26, 2020, 11:07pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/3 "2020-03-26T23:07:21Z")
Thanks, it does the trick!
```julia
import Parameters.with_kw
@with_kw struct Person
name::String
age::Int
end
julia> Person(name="Hugo", age=24)
Person
name: String "Hugo"
age: Int64 24
```
_note_: it also changes the way the structure prints itself, without Parameters.jl, it was
```julia
julia> Person(name="Hugo", age=24)
Person("Hugo", 24)
```
---
### Author:  [@CameronBieganek](https://discourse.julialang.org/u/CameronBieganek)
#### Post date: [March 27, 2020, 12:48am UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/4 "2020-03-27T00:48:10Z")
There’s also `Base.@kwdef`. It’s very poorly advertised, though. It should probably be mentioned in the Constructors chapter in the manual.
---
### Author:  [@bjarthur](https://discourse.julialang.org/u/bjarthur)
#### Post date: [July 9, 2021, 1:17pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/5 "2021-07-09T13:17:22Z")
perhaps `Base.@kwdef` is not documented because it is not exported, is hence considered an internal function, and might be removed in future? seems very useful though. definitely a keeper!
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [July 9, 2021, 1:39pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/6 "2021-07-09T13:39:46Z")
Parameters.jl also export `@unpack`, which is very useful.
---
### Author:  [@pierre-haessig](https://discourse.julialang.org/u/pierre-haessig)
#### Post date: [July 21, 2023, 10:01am UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/7 "2023-07-21T10:01:08Z")
> [@CameronBieganek](#):
>
> There’s also Base.@kwdef. It’s very poorly advertised, though. It should probably be mentioned in the Constructors chapter in the manual.
For the reference, since Julia 1.9 (release April 2023), the `@kwdef` macro is exported, see [Julia 1.9 release NEWS: Standard library changes](https://docs.julialang.org/en/v1.9/NEWS/#Standard-library-changes).
This was implemented in PR
>
>
> Discussed and approved by triage https://github.com/JuliaLang/julia/issues/33192…#issuecomment-1191810619
>
> Fixes https://github.com/JuliaLang/julia/issues/33192
> Fixes https://github.com/JuliaLang/julia/issues/32659
>
> Perhaps this should also close https://github.com/JuliaLang/julia/issues/10146 ?
---
### Author:  [@algunion](https://discourse.julialang.org/u/algunion)
#### Post date: [July 21, 2023, 10:10am UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/8 "2023-07-21T10:10:50Z")
I am only adding this here for context (since the `@kwdef` only appears [documented](https://docs.julialang.org/en/v1/base/base/#Base.@kwdef) in `Base` - so people reading the manual might not easily encounter it).
Please note that by using `@kwdef`, you can also set some defaults for your fields:
```julia
@kwdef struct Person
name::String="World"
age::Int=42
end
```
By defining your `struct` as above, you are also provided with `Person()` constructor (obviously - there are not good defaults for a person, but this can come in handy when defining some configuration or you just have reasonable default values).
---
### Author:  [@pierre-haessig](https://discourse.julialang.org/u/pierre-haessig)
#### Post date: [July 21, 2023, 1:49pm UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/9 "2023-07-21T13:49:29Z")
> [@algunion](#):
>
> I am only adding this here for context (since the `@kwdef` only appears [documented](https://docs.julialang.org/en/v1/base/base/#Base.@kwdef) in `Base` - so people reading the manual might not easily encounter it).
Yes, I opened an issue on this topic ([add at-kwdef to the manual · Issue #32659 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/32659)) but didn’t went to the next level of submitting a PR to add `@kwdef` to the manual.
---
### Author:  [@Lincoln\_Hannah](https://discourse.julialang.org/u/Lincoln_Hannah)
#### Post date: [January 11, 2024, 1:57am UTC](https://discourse.julialang.org/t/automatic-keyword-argument-constructor/36573/10 "2024-01-11T01:57:06Z")
`my_func(; a, b, other... )`
This syntax allows `my_func` to be called with additional arguments that are ignored.
I know you could write a similar constructor for a struct.
It would be nicie if there was a flag that did it automatically. e.g. allow:
```julia
@kwdef @allow_other_args struct X
x::Int
y::Int
end
```
To be created with
```julia
X(x=1, y=2, w=10, z=100, a="something_else" )
```
Use case: I convert a database table to a vector of structs of different types (each row becomes a struct). I currently have to filter the fields of each row to match the struct.
It would be nice to just use `AsTable(:)` to feed each row in as a named tuple and have the requried fields selected automatically.