mirror of
https://github.com/jbranchaud/til
synced 2026-01-03 15:18:01 +00:00
40 lines
1.2 KiB
Markdown
40 lines
1.2 KiB
Markdown
# Requiring Keys For Structs
|
|
|
|
When defining a
|
|
[`struct`](http://elixir-lang.org/getting-started/structs.html) in Elixir,
|
|
we may want to ensure that certain values are provided. We can require that
|
|
certain keys are used in the creation of a struct with the
|
|
[`@enforce_keys`](https://hexdocs.pm/elixir/Kernel.html#defstruct/1)
|
|
attribute. Here is an example of a `Name` struct.
|
|
|
|
```elixir
|
|
defmodule Name do
|
|
@enforce_keys [:first, :last]
|
|
defstruct [:first, :middle, :last]
|
|
end
|
|
```
|
|
|
|
With this defined, we can create a struct that uses all of the keys.
|
|
|
|
```elixir
|
|
> jack = %Name{first: "Jack", middle: "Francis", last: "Donaghy"}
|
|
%Name{first: "Jack", last: "Donaghy", middle: "Francis"}
|
|
```
|
|
|
|
We can also ignore `:middle` and just provide the required keys.
|
|
|
|
```elixir
|
|
> liz = %Name{first: "Liz", last: "Lemon"}
|
|
%Name{first: "Liz", last: "Lemon", middle: nil}
|
|
```
|
|
|
|
We cannot, however, omit any of the keys specified in `@enforce_keys`. If we
|
|
do omit any of them, Elixir will raise an error.
|
|
|
|
``` elixir
|
|
> tracy = %Name{first: "Tracy"}
|
|
** (ArgumentError) the following keys must also be given when building struct Name: [:last]
|
|
expanding struct: Name.__struct__/1
|
|
iex:6: (file)
|
|
```
|