Records, Structs, and Field Updates

A Rust reader brings habits from ownership, enums, traits, Result, modules, pattern matching, and explicit unsafe blocks. That helps with the type that carries the invariant, but the Musi page asks a narrower question: what contract should this field-shaped data example make visible?

struct Pet {
    name: String,
    age: i64,
}

let dog = Pet { name: "Miso".into(), age: 4 };

let Pet := data {
  name : String;
  age : Int;
};

let dog := {
  name := "Miso",
  age := 4,
};
dog.name;

Reading Records, Structs, and Field Updates from Rust

On the Musi side, Musi records and data variants describe stored shape. Behavior belongs in functions or classes/instances, not inside an object by default. Read the shared example through Rust eyes: keep the useful instinct, then let Musi name shape, behavior, absence, and outside work in separate places.

False friend

Do not read class as object shape. If the page is about a pet, invoice, room, or vehicle, start with fields or variants. For a Rust reader, the trap is expecting Musi syntax to mirror Rust even when the ideas are separated differently; Musi class is closest to a Rust trait plus law text; instances play the role of implementations for behavior.

When this pays off

Use records when names like owner, age, amount, or route are the point of the value. The Rust instinct still helps here: Keep the Rust habit of asking which type carries the invariant.

Keep close

• Records
• Classes
• Patterns