Function insert_with 

pub fn insert_with<T, F>(
    component_fn: F,
    mode: InsertMode,
) -> impl EntityCommand
where
    T: Component,
    F: FnOnce() -> T + Send + 'static,

An EntityCommand that adds a component to an entity using some function that returns the component.

The function will only be invoked if the component will actually be inserted. In other words, the function will not be invoked if mode is InsertMode::Keep and the entity already has the component.