Cacher | Super simple caching solution for iOS , macOS , tvOS | iOS library

I'm going through the Rust book and I'm currently a bit confused about my solution to the exercise in Chapter 13 on closures (https://doc.rust-lang.org/book/ch13-01-closures.html).

I want to apologise in advance if my questions don't make much sense. I still have a lot of things to learn. If my questions are too broad, please feel free to point me to specific documentation.

The code seems to run fine but I don't really understand the following:

1. Why does self.map.get() take a reference? The map field is of type HashMap and this doesn't take a reference but u32.
2. Do I always need to use Some(v) and None under match?
3. Why do I need to dereference *v?

As recommended in Chapter 13.1, i tried to implement a Cacher using HashMap:

I want to change the text when filling or unfolding the accordion. I'm on Bootstrap 4.

Currently it works, but the first time the page loads, the button text is not correct.

If I unfold and fold, the text is correct.

Why is this not the right text when the page loads ?

index.html :

Being an aspiring rustacean, I've been working my way through The Rust Programming Language book and being in the 13th chapter I was attempting to generalize the Cacher struct, that has as a purpose implementing lazy evaluation around a closure. While I was able to use generics to generalize the closure signature to any one parameter with any one output type, I can't figure out how to generalize this to closures with any number of params. I feel like there should be a way to do this.

I have been studying the official rust book, in the chapter on "closures" there is a demonstration of how to use cache with rust using structs and impl, then at the end they say that we add functions to the code, one of them start to use a dictionary so that we can have a multiple cache, I did that quickly, but then it says:

The second problem with the current Cacher implementation is that it only accepts closures that take one parameter of type u32 and return a u32. We might want to cache the results of closures that take a string slice and return usize values, for example. To fix this issue, try introducing more generic parameters to increase the flexibility of the Cacher functionality.

the relevant part of the code right now, with my modifications it looks like this.

Apologies for the following question. The compiler says that a temporary is created which is freed while still in use.

What I was trying to do is an example from the Rust book at https://doc.rust-lang.org/book/ch13-01-closures.html in which a Closure is supposed to update a HashMap in case the searched key is not found.

How can make this code compilable? Playground:

Every time I edit the code new errors arise, even following recommendations from the compiler.

I am trying to create a Cacher struct which will store calculated values in a HashMap. The calculation method will take one variable of type T, do calculations and return a value with the same type T. The type for this calculation callback will be Fn(T) -> T.

I figured out that value which will be a key of HashMap has to implement the Eq and Hash traits. It looked like everything should be working and I could compile my program without errors.

Then I wrote one test to check everything works as expected:

The problem is that my generic type T only accepts arguments from u32 and in this case I am trying to pass a generic value that I store in U.

Is there a way to cast generics to a specific type? What can I do to solve the problem?

I have a service worker that should return a cached file if it's of a certain type. If not, it should fetch the resource. I put the code that checks if the file is a certain type inside the fetch function. If it is, it returns the cached version. If not, it returns the fetched version. I have found out though, that it sends a network request for the fetch, then returns the cached version (duh).

I don't want this because it undos the purpose of serving the cached version of a large file instead of fetching it if possible. I realized I have to put the if then statement outside of the fetch, but that would mean that I am putting it in as a parameter. This is a problem, because it throws an error. So, I decided to put it inside a function. This returns an invalid response, so I don't know what I am doing wrong. It must be that the function inside the event.respondWith() must not be returning, but why?

My code is: