Messages

One of the two main types in DependoBuf is a message type. Message declaration consists of a keyword message, followed by a type identifier, followed by optional type dependencies, followed by a block of field declarations.

\[ \begin{align*} type\_dependency ::=&\ \texttt{(}\ type\_variable \texttt{)}\\ message\_definition ::=&\ \texttt{message}\ type\_identifier \ \lbrace type\_dependency \rbrace\ \texttt{\{}\ \lbrace typed\_variable \rbrace\ \texttt{\}} \end{align*} \]

Example message declaration

message User (n Unsigned) {
  name String
  id Unsigned
  age Int
  active Bool
  friends Vec User n
}

Compiler will generate a constructor for each message type with the same name as the message itself. Because a message has only one constructor, you can use dot notation to access fields of a message.

Example message usage

message Foo {
  bar Int
}

message Baz (n Int) {}

message Quux {
  foo Foo
  baz Baz foo.bar
}

In this example you also see that you can use an already declared field as a variable in another field declaration.

When creating a value of type Quux and initializing its fields you will have to provide such a value for the baz field that its type parameter n matches the bar field of the value you provided for the foo field. But don't worry, as all this will be checked by the compiler and you will get a compile-time error if you try to create a value that doesn't match the expected type.