Crate anymore

The Anymore crate provides the AnyDebug trait, for dynamically typed values which can be inspected in Rust.

These can be used in any program domain, but have been developed with graphical user interface libraries as the target consumer. The AnyDebug trait also has the type_name method, which can be used to access the type name of the contained value.

Usage

The traits in this crate can be used in the same way that you would use Any, with the additional capability that the Debug implementation is meaningful. See the module-level documentation of Any for more details of how it can be used.

Smart pointers and dyn AnyDebug

When you have dyn AnyDebug contained in a smart pointer, such as Box or Arc, the type_name method will give the type name of the smart pointer, rather than the type name of the contained value. This can be avoided by converting the smart pointer into a &dyn AnyDebug instead, which will return the object’s type name. This is the same caveat seen with thetype_id method on Any.

Motivation

In user interface contexts, there is often a need for passing dynamically typed values. In Xilem, for example, one of the key concepts is dispatching arbitrary messages to the correct component (called View in Xilem). Each View expects messages of a specific type or types, and knows how to handle these. However, sometimes, due to bugs elsewhere in the app, a view will receive a message of a type it didn’t expect. If it were using the standard library, Any type, there would be no feasible way for the author of that View implementation to learn what the underlying type was. This can make understanding this failure quite challenging. Because of this, Xilem uses the AnyDebug trait for these messages, so they can be inspected.

A similar need arises in Masonry, which is the widget toolkit co-developed with Xilem.

Feature Flags

The following crate feature flags are available:

• alloc (enabled by default): Implement downcasting from Boxes. If this feature is not enabled, Anymore can be used in contexts without an allocator enabled.
• type_name (enabled by default): Provide the type_name function on AnyDebug, which gives the type’s name. Most users should leave this enabled, as the costs of this method existing are expected to be negligible.

Traits

AnyDebug

A trait to implement dynamic typing.