Proposed Casher struct is in directory proposed_edition #18
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src/proposed_addition/casher.rs
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| pub fn value(&mut self, arg: U) -> V { |
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It should be possible to do a single lookup using the Entry API:
self.values.entry(arg).or_insert_with_key(self.calculation)
Note that for this to work, the version number in .travis.yml will have to be updated to 1.50.
calculation will then take &U, so we would no longer need U: Copy. If you don't want it to take &U, here's an alternative implementation:
self.values.entry(arg).or_insert_with_key(|&key| self.calculation(key))
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These are all great edits! I'll get to them when I get back to my computer late tonight, I was running out the door when I submitted this! |
src/cashing.rs
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| /// let sixteen = squared.on(4); | ||
| /// ``` | ||
| pub fn on(&mut self, arg: U) -> V { | ||
| // Clippy doesn't like that this isn't lazy but I'm fine with it. |
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I think clippy complains because you'll be doing the computation even if the result is already cached, since arguments are always evaluated before a function (e.g., or_insert) is called.
Did you have any luck with or_insert_with_key? It takes a closure, which doesn't actually perform the computation unless called.
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I ran into borrow problems since we take a mutable reference to self. I'll retry implementing it and if I can't make it work I'll follow up here.
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So after fighting for a bit, I didn't really run into anything I would consider a clean readable solution. I am pushing with a solution that doesn't use the entry api. It's a little longer, but I think very readable. I'm as in love with the entry api as the next guy, so let me know if this isn't acceptable.
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In that case, it's good as is. I might give Entry another try later :)
src/cashing.rs
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| /// reads from a file and | ||
| /// you think the contents of that file have changed even though the name | ||
| /// has not. | ||
| pub fn call_and_replace(&mut self, arg: U) -> V { |
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Hm this might be useful for a small number of users. In the name of conciseness, I'm not sure yet if I'd keep this feature in the long-term, since simple problems like those in competitions shouldn't have this kind of state-dependence. Anyway, for now I'll keep it however you decide.
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Even if it doesn't make sense for use in competition, I think this function makes a lot of sense for the structure. I can see it being used with rand in clever ways as well.
Let me know what you think about adding this sort of small patterns material!