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typed struct #2

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typed struct #2

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31 changes: 31 additions & 0 deletions draft-kohbrok-mls-implementation-considerations.md
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Expand Up @@ -45,6 +45,37 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
document are to be interpreted as described in BCP 14 {{RFC2119}} {{!RFC8174}}
when, and only when, they appear in all capitals, as shown here.

# Typed structs
In many places, MLS uses a typed pattern of structs, where we have a type `uint`,
followed by a `select` statement that decides the type of the following field based on the preceding type `uint`.
For example the Credential struct:

```
struct {
CredentialType credential_type;
select (Credential.credential_type) {
case basic:
BasicCredential;

case x509:
Certificate chain<1..2^32-1>;
};
} Credential;
```

Other examples are `Content`/`ContentType`, `PSKType` in `PreSharedKey`, `Sender`/`SenderType` and `Proposal`/`ProposalType`.

We can generalise this into a typed struct as follows:

```
struct {
T type;
select(typed<T>.type) {
T.variant1:
Variant1
}
} typed<T>
```

# Security Considerations

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