This function wants to log its parameter out prior to doing work with it. Hereâs an example: you want to model the employees of some company, and Employee seems a. When we have a Box, we have access to both of those functions, but we can also call a plain downcast function to move the contained value out of.The GoF said Prefer Composition to Inheritance in their Design Patterns book, twenty-two years ago. Logger function for any type that implements Debug. A common problem with object-oriented design is trying to force things into a is-a relationship, and neglecting has-a relationships. We don't know the concrete type of our value at compile time, so we need to We want to give special treatment to certain types: in thisĬase printing out the length of String values prior to their value. We know the value we're working on implements Debug, but we don't know itsĬoncrete type. Most types implement Any.However, any type which contains a non-static reference does not.See the module-level documentation for more details. ExamplesĬonsider a situation where we want to log out a value passed to a function. This is needed since Rust cannot generate &mut Anyâs vtable from &mut Traitâs. Box can then be further downcast into Box where ConcreteType implements Trait. Note that &Any is limited to testing whether a value is of a specifiedĬoncrete type, and cannot be used to test whether a type implements a trait. Convert Box (where Trait: Downcast) to Box. However, any type which contains a non- static reference does not.See the Box documentation for the full details. any This module contains the Any trait, which enables dynamic typing of any static type through runtime reflection. Trait object downcasting support using only safe Rust. Box adds the downcast method, which attempts toĬonvert to a Box. Trait for downcasting trait objects back to their original types. Is also the downcast_mut method, for getting a mutable reference to the It currently supports bits, unsigned integers, and signed integers. As &Any (a borrowed trait object), it has the is andÄowncast_ref methods, to test if the contained value is of a given type,Īnd to get a reference to the inner value as a type. Typenum is a Rust library for type-level numbers evaluated at compile time. Of any 'static type through runtime reflection.Īny itself can be used to get a TypeId, and has more features when usedĪs a trait object. This module implements the Any trait, which enables dynamic typing
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