Macro late_struct 

macro_rules! late_struct {
    (
        $($ty:ty $(=> $erase_to:ty)?),*
        $(,)?
    ) => { ... };
}

Implements the LateStruct trait for the specified $ty type, turing it into a marker type that can be used to refer to a late-initialized structure.

See the crate level documentation for examples of this macro in action as well as a step-by-step guide on how to use it.

You can attach fields onto this type using the late_field! macro and can instantiate the structure defined by this macro using the LateInstance struct. Either operation can occur anywhere within the crate graph of a project; fields can be added to the structure in crates which are downstream to crates which instantiate that structure.

The $ty type need only be Sized and live for 'static. No types in this macro invocation may involve unbound generic parameters.

You can specify more than one type onto which LateStruct should be implemented with this macro.

The EraseTo Parameter

The optional $erase_to type specifies the type all field values should be able to upcast (i.e. “erase”) to. Generally, this type is a trait object. For instance, if you specify dyn Any + Send + Sync, all field values will have to implement Any, Send, and Sync. If $erase_to is omitted, the type will default to dyn 'static + fmt::Debug, which would entail that all fields in the struct must implement the Debug trait.

In addition to the trait constraints $erased_to places on fields, late_field! automatically enforces that all fields live for 'static, be Sized, and implement the Default trait. It is this Default trait implementation which is used to initialize instances of this struct.

Traits such as Eq, Clone, and Hash are not dyn compatible and thus cannot be used directly inside the bounds of the $erase_to type. You can work around this restriction by using the DynEq, DynClone, and DynHash traits respectively, which are dyn compatible while still encoding the necessary constraints.