There is no general way of knowing the type of something, your values are just bytes in memory without any metadata. In Rust, types are mostly a compile-time concept, they don’t really exist when your program is running. This function wants to log its parameter out prior to doing work with it. In dynamic languages, downcasting is trivial thanks to runtime reflection, more specifically, runtime metadata about types. You could make it work by using an enum that has a variant for every supported animal type. Ultimately though, 'boxed any' might not the best solution for what you are trying to accomplish. Logger function for any type that implements Debug. asref (.) to get a reference to the data inside the box and use. 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. New York State Department of Environmental Conservation (DEC) is now selling hunting and trapping licenses and Deer Management Permits (DMPs) for the 2022. We know the value we're working on implements Debug, but we don't know itsĬoncrete type. ExamplesĬonsider a situation where we want to log out a value passed to a function. 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. See the Box documentation for the full details. Box adds the downcast method, which attempts toĬonvert to a Box. Is also the downcast_mut method, for getting a mutable reference to the As &Any (a borrowed trait object), it has the is andĭowncast_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. 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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