# `Ethers.TypedData.Domain`
[🔗](https://github.com/ExWeb3/elixir_ethers/blob/v0.8.0/lib/ethers/typed_data/domain.ex#L1)

The EIP-712 domain separator data (`EIP712Domain`).

The domain scopes a signature to a particular application, contract and chain so that a
signature produced for one domain cannot be replayed in another. All five standard fields are
optional and only the fields that are actually present (non-nil) participate in the domain
type - this matches the behaviour of ethers.js / MetaMask and is required for interoperability.

Standard fields (in canonical EIP-712 order) and their Solidity types:

| Field                | JSON name           | Solidity type |
| -------------------- | ------------------- | ------------- |
| `:name`              | `"name"`            | `string`      |
| `:version`           | `"version"`         | `string`      |
| `:chain_id`          | `"chainId"`         | `uint256`     |
| `:verifying_contract`| `"verifyingContract"`| `address`    |
| `:salt`              | `"salt"`            | `bytes32`     |

## Example

    Ethers.TypedData.Domain.new(
      name: "Ether Mail",
      version: "1",
      chain_id: 1,
      verifying_contract: "0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC"
    )

# `t`

```elixir
@type t() :: %Ethers.TypedData.Domain{
  chain_id: non_neg_integer() | nil,
  name: String.t() | nil,
  salt: binary() | nil,
  verifying_contract: Ethers.Types.t_address() | nil,
  version: String.t() | nil
}
```

An EIP-712 domain. Every field is optional (`nil` when absent).

- `name` - human readable name of the signing domain (`string`).
- `version` - current version of the signing domain (`string`).
- `chain_id` - the EIP-155 chain id (`uint256`).
- `verifying_contract` - address of the contract that will verify the signature (`address`).
- `salt` - a disambiguating 32-byte salt (`bytes32`).

# `new`

```elixir
@spec new(t() | map() | keyword()) :: t()
```

Creates a new `Ethers.TypedData.Domain` from a keyword list or a map.

Accepts atom keys (`:chain_id`) or string keys (`"chain_id"`). An existing
`Ethers.TypedData.Domain` struct is returned unchanged. Unknown keys are ignored.

## Examples

    iex> Ethers.TypedData.Domain.new(name: "Ether Mail", version: "1", chain_id: 1)
    %Ethers.TypedData.Domain{name: "Ether Mail", version: "1", chain_id: 1}

# `present_fields`

```elixir
@spec present_fields(t()) :: [Ethers.TypedData.Field.t()]
```

Returns the present (non-nil) domain fields in canonical EIP-712 order as a list of
`Ethers.TypedData.Field` structs.

Each returned `Field` uses the JSON field name (e.g. `"chainId"`) and its Solidity type. Only
fields that are set participate in the `EIP712Domain` type - absent fields are omitted. This
is consumed by both the JSON serializer and the hashing engine in later stages.

## Examples

    iex> Ethers.TypedData.Domain.new(name: "Ether Mail", chain_id: 1)
    ...> |> Ethers.TypedData.Domain.present_fields()
    [
      %Ethers.TypedData.Field{name: "name", type: "string"},
      %Ethers.TypedData.Field{name: "chainId", type: "uint256"}
    ]

---

*Consult [api-reference.md](api-reference.md) for complete listing*