Structs

In Flame, data structures and their behavior are cleanly decoupled: struct defines the data shape and memory layout, while impl defines associated functions and methods.

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Defining a Struct

Declare a struct with named, typed fields:

struct User {
    id: Int,
    name: String,
    email: String,
    is_admin: Bool
}

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Instantiating Structs

You can create an instance of a struct by specifying its field values:

let user = User {
    id: 101,
    name: "Samantha",
    email: "samantha@example.com",
    is_admin: true
}

print(user.name)       // "Samantha"
print(user.is_admin)   // true

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Mutable Struct Instances

If you declare a struct variable with let mut, you can update its fields in-place:

let mut session = User {
    id: 1,
    name: "Guest",
    email: "guest@example.com",
    is_admin: false
}

// Mutate fields
session.name = "Admin"
session.is_admin = true

print(session.name) // "Admin"

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Nested Structs

Structs can freely embed other custom structs, formulas, or vectors:

struct GeoLocation {
    lat: Float,
    lng: Float
}

struct Company {
    name: String,
    location: GeoLocation,
    employees: Vec<User>
}

let office = Company {
    name: "Flame Tech",
    location: GeoLocation { lat: 37.7749, lng: -122.4194 },
    employees: [user]
}

print(office.location.lat) // 37.7749

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Deserializing Structs

Flame provides built-in .fromJson() and .fromBytes() methods on all struct type definitions. This allows you to easily parse JSON strings or binary UTF-8 byte payloads directly into a typed struct instance.

struct Config {
    port: Int,
    host: String
}

// Parse from a JSON string
let cfg1 = Config.fromJson('{"port": 8080, "host": "localhost"}')
print(cfg1.port) // 8080

// Parse from raw bytes (e.g., from an HTTP response or file)
let raw_bytes = "{\"port\": 3000, \"host\": \"0.0.0.0\"}".toByte()
let cfg2 = Config.fromBytes(raw_bytes)
print(cfg2.host) // "0.0.0.0"

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Next Steps

To add methods and constructors to your structs, explore Impl & Methods.