Elixir Struct definition

Question

Structs are extensions built on top of maps. However, I was expecting the struct definition to be like,

defmodule User do
  defstruct %{name: "John", age: 27}
end

However, I was surprised find that the fields need to be defined as Keyword Lists.

defmodule User do
  defstruct [name: "John", age: 27]
end

I find this odd, is there a reason for this notation?

Hauleth · Accepted Answer · 2018-03-24 13:41:09Z

3

Because it allows you to use 2 different notations:

defstruct [:name, :age]

if there is no default value or:

defstruct [name: "John", age: 27]

if there are default values. You can even mix these two:

defstruct [:name, age: 27]

Additional if you use keyword list you can omit [] which is sometimes handy.

answered Mar 24, 2018 at 13:41

Hauleth

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1 Comment

BlueGene Over a year ago

I see, so it looks like it is purely for syntactic sugar. I also just found out that you can do this when declaring maps: ` %{name: "John", name: "Jose", age: 27}`

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