If we wanted to call some methods from DynData (the trait in the example isÄ®mpty, but pretend Iâve put some method in there too), we would be out of luck. Well, only if the DynData didnât have any methods we would still want to call. So, instead of keeping Arc, we could keep Arc, right? I didnât feel comfortable with that even though the code there is The above in a crate, but it hasnât been updated for 4 years and seems We could use mopa instead, as it simply wraps After all, itâs what downcast_ref doesÄ«ut letâs assume we are not really comfortable with such approach. #! from our projectâs header and prove that we didnât make anyĪccidental mistakes (like extending a lifetime past its expiration date orĬreating multiple mutable references). Then we can just cast the pointers around aÄ«it, read the Rustonomicon, read the Unsafe guidelines, remove We do have the type_id, so we can check if the When one is willing to use these heavy hammers, it is possible to just implementÄowncast_ref ourselves. So, what can we do? The big hammer â use unsafe Therefore the data.downcast_ref() wonât compile. Methods are specifically for dyn Any or Box. If you paid a very close attention, youâve noticed that all the downcasting Virtual table) must have the same signature no matter what the real type ofÄ®num Either // A lot more boilerplate. Would make the caller really confused â all methods (dispatched through the In particular, it disallows using Self and associated types as these ![]() To actually exist, the trait X canât be too rich (this is called [object ![]() Only through pointers (boxes, Arcs, references, â¦). This makes it hard to manipulate â it canât be stored on stack, While dyn X is a type in its own right, it has an unknown size duringĬompilation. Vtables â lookup tables that are used to decide what method implementation toĬall on that particular value. The values directly, but stores pointers to the data together with pointers to The solution comes in the form of dynamic dispatch. To put both As and Bs into the same HashMap or Vec. Have a trait X and types A and B, static dispatch wonât help if you want The downside is, everything all the way up needs to be monomorphized. Which might eventually produce slightly faster result. ItĪlso knows what exact method will be called, which means they can be inlined, Most importantly, it knows how large the values are to store them on stack. Types everywhere can be substituted and the compiler knows how to handle them â This gives one a lot of flexibility, because the The compiler copy-pastes the code and substitutes The first, more common one, is through monomorphization, also called There are two general approaches to handling values of distinct types uniformly I canât show the actual full final code (itâs not open source), but Iâm sharing Some way (I donât have a specific proposal, only a pain point). Particular thing easier by improving the standard library or the compiler in Maybe someone would also get inspired and figure out a solution to make this Solution, eventually, and youâre free to get inspired by it), it might be a goodÄ®ntertainment for some (some people like to read about othersâ difficulties) and Sharing this partly because it might save someone some time (I did find a Have settled our differences on that one already, but about downcasting. This dialogue was not about the lifetimes and borrowing, we (me and rustc) The notion of fight and would prefer to call it a dialogue or maybe aÄispute, this story shows the particular activity is not restricted only to ![]() After that initial refresh it obeys the rules that I have created.It is said that Rust beginners fight the compiler. My only complaint is that on installing and turning on icloud, the app downloaded podcasts from pods forwhich I have disabled autorefresh. Note that this dude is supporting the app as a side gig on his own so he does not do feature requests. In the past I have reached out to the developer by email and he quickly responded. RefCell implements Any, so one approach would be to store that inside Rc and then use Rc::downcast:: to recover the cell.You can import mp3 and m4a files to create your own "podcast" collection, and autopopulating playlists allow for amazing control over how multiple episodes from different pods are delivered for driving etc. It allows adjustment in playback location to skip ads and bumper music at the begining and end of the episode. It allows play speeds in 1/4x increments from 1/2 to 3x. This is my first time using the app on my laptop and it runs fine, when I turned on icloud sync all of my podcasts from my phone were transfered to my Pc.Äowncast is a superior podcasting app as it provides an enormous amount of user control over how the app handles (1) your podcast library, (2) individual podcast behavior, and (3) individual episode behavior. I own this app on my iPhone 6 and a 2021 PC.
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