Add Len() to common interface

[norri]

Len() method is useful in common interface and is simple to implement.

• implement Len for simple cache, it was the only policy missing the method

Fixes #43

[Code-Hex]

Should add method of the Cache struct because this is breaking change.

I think good like below:

Len() int { return len(c.Keys()) }

[norri]

Do you mean that this my change below:

func (c *Cache[K, V]) Len() int {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.cache.Len()
}

should be changed to:

func (c *Cache[K, V]) Len() int {
	return len(c.Keys())
}

[Code-Hex]

@norri Yes!

[norri]

I think performance for c.cache.Len() is better than len(c.Keys()) because of for example sorting is not needed and all policies support Len(). However I can make the change if you think that it's better.

[Code-Hex]

Could you measure the performance?
And also please implement all cache policies not just simple 🙏

I think this discussion is required all cache policies results.

I think performance for c.cache.Len() is better than len(c.Keys())

[norri]

I can try to test the performance. All other policies implement already Len() so no changes needed for those.

[norri]

I added benchmark test for both implementations and using just Len() is quite match faster:

$ go test -benchmem -bench BenchmarkLenWithKeys ./policy/simple
goos: darwin
goarch: amd64
pkg: github.com/Code-Hex/go-generics-cache/policy/simple
cpu: Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz
BenchmarkLenWithKeys-8           3777514               310.7 ns/op           104 B/op          3 allocs/op
PASS
ok      github.com/Code-Hex/go-generics-cache/policy/simple     1.640s

$ go test -benchmem -bench BenchmarkJustLen ./policy/simple
goos: darwin
goarch: amd64
pkg: github.com/Code-Hex/go-generics-cache/policy/simple
cpu: Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz
BenchmarkJustLen-8      1000000000               0.3075 ns/op          0 B/op          0 allocs/op
PASS