`Cache` missing `Debug` impl about moka HOT 3 CLOSED

If it's easy enough to show those and won't be too expensive then that sounds fine to me. It just bothered me that my type that has a cache couldn't show anything at all about it.

It looks like #134 is adding methods to query for these stats, which I appreciate as it means I have the option of showing those after all if it suits my usage better.

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I'm not sure what offhand such an impl should show, but perhaps some basic stats about the cache if that's easy to gather.

I started to work on this as #134 and made the Debug impl to show some basic stats. But while I was writing a code sample for the doc, I realized this will confuse users as these stats are eventual consistent (will show stale numbers).

use moka::sync::Cache;
​
let cache = Cache::new(10);
​
// Insert entries.
cache.insert('n', "Netherland Dwarf");
cache.insert('l', "Lop Eared");
​cache.insert('d', "Dutch");

// Ensure an entry exists.
assert_eq!(cache.get(&'l'), Some("Lop Eared"));
​
// Print a debug info. Note that this may print stale numbers.
// (e.g. `entry_count` can be `0` instead of `3`)
println!("{:?}", cache);
// -> Cache { max_capacity: Some(10), entry_count: 0, weighted_size: 0 }
​
// You can mitigate this by performing a `sync` first.
// Bring `ConcurrentCacheExt` trait to the scope so we can use `sync` method.
use moka::sync::ConcurrentCacheExt;
// Call `sync` to run pending internal tasks.
cache.sync();

// Now it will print the actual numbers.
println!("{:?}", cache);
// -> Cache { max_capacity: Some(10), entry_count: 3, weighted_size: 3 }

These are kept eventual consistent to improve performance (doc).

So I think I will change it to show key-value entries like the Debug impl of std::collections::HashMap does. It will be something like:

use moka::sync::Cache;
​
let cache = Cache::new(10);
​
// Insert entries.
cache.insert('n', "Netherland Dwarf");
cache.insert('l', "Lop Eared");
​cache.insert('d', "Dutch");

// Print a debug info.
println!("{:?}", cache);
// -> {'l': "Lop Eared", 'd': "Dutch", 'n': "Netherland Dwarf"}
// Note that entries are returned in arbitrary order.

This will never show stale values, so it will not confuse users.

To show key-value entries, both K and V must implement Debug. I hope you are okay with this.

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Hi @lilyball — I have published Moka v0.8.5 to crates.io containing this and some other changes. Thanks!

• CHANGELOG Version v0.8.5

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