Derive Macro FmuModel 

#[derive(FmuModel)]
{
    // Attributes available to this derive:
    #[model]
    #[variable]
    #[alias]
    #[child]
}

FmuModel derive reference

Struct-level attributes

Use #[model(...)] on the struct to configure the generated FMI interfaces and metadata.

#[derive(FmuModel, Default)]
#[model(
    description = "Example FMU",
    model_exchange = true,
    co_simulation = false,
    scheduled_execution = false,
    user_model = true,
)]
struct MyModel {
    #[variable(causality = Output, start = 1.0)]
    y: f64,
}

Supported keys:

• description: Optional string. Defaults to the struct docstring if omitted.
• model_exchange: Optional bool. Defaults to true.
• co_simulation: Optional bool. Defaults to false.
• scheduled_execution: Optional bool. Defaults to false.
• user_model: Optional bool. Defaults to true. Set false to provide your own impl UserModel.

Notes:

• All boolean flags must be explicit (co_simulation = true). Shorthand co_simulation is rejected.
• #[model()] with no arguments is valid and uses the defaults above.

Field-level attributes

Use #[variable(...)] to include a field as an FMI variable. Use #[alias(...)] for additional aliases. Both attributes accept the same keys.

#[derive(FmuModel, Default)]
struct MyModel {
    /// Height above ground
    #[variable(causality = Output, start = 1.0)]
    h: f64,

    /// Velocity of the ball
    #[variable(causality = Output, start = 0.0)]
    #[alias(name = "der(h)", causality = Local, derivative = h)]
    v: f64,
}

Supported keys for #[variable(...)] and #[alias(...)]:

• skip: Bool. When true, the field is ignored for FMI variables.
• name: String. Overrides the variable name (defaults to the field name).
• description: String. Overrides the field docstring.
• causality: One of Parameter, CalculatedParameter, Input, Output, Local, Independent, Dependent, StructuralParameter.
• variability: One of Constant, Fixed, Tunable, Discrete, Continuous.
• start: Rust expression used as the start value.
• initial: One of Exact, Calculated, Approx.
• derivative: Ident referencing another field. Marks this variable as the derivative of that field.
• event_indicator: Bool. When true, counts toward the FMI event indicator total.
• interval_variability: One of Constant, Fixed, Tunable, Changing, Countdown, Triggered.
• clocks: List of clock field idents that this variable belongs to.
• max_size: Integer. Max size for Binary variables.
• mime_type: String. MIME type for Binary variables.

Notes:

• Continuous state variables are inferred by derivative relationships.
• clocks must reference clock variables in the same model. The generated FMU resolves these to value references.

Child components

Use #[child(...)] to reuse another FmuModel as a component and prefix its variable names.

#[derive(FmuModel, Default)]
struct Parent {
    #[child(prefix = "bus")]
    bus: CanBus,
}

Supported keys:

• prefix: Optional string. Defaults to the field name. Child variables are named <parent_prefix><prefix>.<child_variable>.

Notes:

• Child fields should implement the Model trait (typically via FmuModel).
• #[child] only affects naming and metadata; it does not change runtime behavior of the child component. Main derive macro for FMU models

Example

use fmi_export::FmuModel;

/// Simple bouncing ball model
#[derive(FmuModel, Default)]
#[model()]
struct BouncingBall {
    /// Height above ground (state output)
    #[variable(causality = Output, start = 1.0)]
    h: f64,

    /// Velocity of the ball
    #[variable(causality = Output, start = 0.0)]
    #[alias(name="der(h)", causality = Local, derivative = h)]
    v: f64,
}