Structs

struct MyStruct {
    a int,
    b string,
}

Arbitrary struct types can be defined in struct blocks. To use these types in parameters, fields, or return types, use struct ❮name❯. e.g.

function foo(s struct MyStruct) { ... }
function makeStruct() struct MyStruct { ... }
struct InteriorStruct { thing struct MyStruct }

Any type may be used for struct fields except opaque types, though further restrictions may be enforced when the structs are used with publish and emit statements.

Struct Definition Field Insertion

When defining a struct, you can refer to a previously defined struct to insert those field definitions into your struct. For example, this:

struct Foo {
    a int,
    b bool,
}

struct Bar {
    +Foo,
    c string,
}

Defines Bar equivalently to specifying fields a, b, and c explicitly. This also works in command fields:

command Baz {
    fields {
        +Bar,
        d optional bytes,
    }
    ...
}

As well as effects. Fields are inserted in the order specified by the referenced struct. Expansion happens as the struct is compiled. You can only refer to a struct that has been previously defined (though because commands may be compiled in a later pass, all structs may be defined at that point). Multiple references can be made, and they can be inserted anywhere in the struct.

Duplicate fields from referenced struct definitions are a compile error, e.g.

struct A { x int }
struct B { +A, x int }

Struct B will cause an error because x is already defined in A.