Attribute Macro system 

#[system]

Marks a function as a system

Validates that the function has the correct signature for a system:

• Exactly one parameter
• Parameter type must be &mut Context

This macro doesn’t transform the function, it only validates at compile time. The actual system registration happens via add_system() or add_startup_system().

Example

#[system]
fn movement(ctx: &mut Context) {
    ctx.world_mut()
        .select_mut::<(Position, Velocity)>()
        .each(|_, (pos, vel)| {
            pos.x += vel.x;
        });
}

Errors

Compile error if:

• Function has zero or multiple parameters
• Parameter is not &mut Context