Static value

Static values are useful in case of clear declaration and validation in general but super useful for dispatching variants dynamically. This behaviour will be explained more detail in variant_of docs section.

You don't need to pass static values when creating new struct and they are validated upon parsing. Static values are not stored in any way but always inlined instead.

Inline bytes

iex> defmodule StructInlineBytes do
...>   use BinStruct
...>   field :value, <<1, 2, 3>>
...> end
...>
...> StructInlineBytes.new()
...> |> StructInlineBytes.dump_binary()
...> |> StructInlineBytes.parse()
...> |> then(fn {:ok, struct, _rest } -> struct end)
...> |> StructInlineBytes.decode()
%{ value: <<1, 2, 3>> }
copy

Optional

iex> defmodule StructOptionalStaticValueNotPresent do
...>   use BinStruct
...>   field :value, <<1, 2, 3>>, optional: true
...> end
...>
...> StructOptionalStaticValueNotPresent.new()
...> |> StructOptionalStaticValueNotPresent.dump_binary()
...> |> StructOptionalStaticValueNotPresent.parse_exact()
...> |> then(fn {:ok, struct } -> struct end)
...> |> StructOptionalStaticValueNotPresent.decode()
%{ value: nil }

iex> defmodule StructOptionalStaticValuePresent do
...>   use BinStruct
...>   field :value, <<1, 2, 3>>, optional: true
...> end
...>
...> StructOptionalStaticValuePresent.new(value: :present)
...> |> StructOptionalStaticValuePresent.dump_binary()
...> |> StructOptionalStaticValuePresent.parse_exact()
...> |> then(fn {:ok, struct } -> struct end)
...> |> StructOptionalStaticValuePresent.decode()
%{ value: <<1, 2, 3>> }
copy

Inline bitstring

iex> defmodule StructInlineBitstring do
...>   use BinStruct
...>   field :first, <<1::1, 1::1, 1::1, 1::1>>
...>   field :second, <<0::1, 0::1, 0::1, 0::1>>
...> end
...>
...> StructInlineBitstring.new()
...> |> StructInlineBitstring.dump_binary()
...> |> StructInlineBitstring.parse()
...> |> then(fn {:ok, struct, _rest } -> struct end)
...> |> StructInlineBitstring.decode()
%{ first: <<1::1, 1::1, 1::1, 1::1>>, second: <<0::1, 0::1, 0::1, 0::1>> }
copy

Inline String.t

iex> defmodule StructInlineString do
...>   use BinStruct
...>   field :value, "123"
...> end
...>
...> StructInlineString.new()
...> |> StructInlineString.dump_binary()
...> |> StructInlineString.parse()
...> |> then(fn {:ok, struct, _rest } -> struct end)
...> |> StructInlineString.decode()
%{ value: "123" }
copy

Evaluated

iex> defmodule StructWithEvaluatedStaticValue do
...>   use BinStruct
...>
...>   @my_static_constant <<1, 2, 3>>
...>
...>   field :v1, { :static, @my_static_constant }
...>   field :v2, { :static, BinStruct.PrimitiveEncoder.uint8(1) }
...>
...> end
...>
...> StructWithEvaluatedStaticValue.new()
...> |> StructWithEvaluatedStaticValue.dump_binary()
...> |> StructWithEvaluatedStaticValue.parse()
...> |> then(fn {:ok, struct, _rest } -> struct end)
...> |> StructWithEvaluatedStaticValue.decode()
%{ v1: <<1, 2, 3>>, v2: <<1>> }
copy