列出软件包`MoveToFront`对我不起作用

Question

New to Go and building a simple LRU cache in Go to get used to syntax and Go development.

Having an issue with the MoveToFront list method, it fails on the following check in the MoveToFront body

if e.list != l || l.root.next == e 

I want to move the element (e) to the front of the list when I retrieve it from cache , like this

if elem, ok := lc.entries[k]; ok {
    lc.list.MoveToFront(elem) // needs fixing
    return elem
}
return nil

The Code can be seen here on line 32 the issue occurs

https://github.com/hajjboy95/golrucache/blob/master/lru_cache/lrucache.go#L32

Answer 1

There seem to be two problems, to me. First, this isn't how the List data type is meant to be used: lc.list.PushFront() will create a List.Element and return a pointer to it. That's not fatal, but at the least, it is kind of annoying—the caller has to dig through the returned List.Element when using Get, instead of just getting the value.

Meanwhile, presumably the failure you see is because you remove elements in Put when the LRU-list runs out of space, but you don't remove them from the corresponding map. Hence a later Put of the just-removed key will try to re-use the element in place, even though the element was removed from the list. To fix this, you'll need to hold both key and value. (In my simple experiment I did not see any failures here, but the problem became clear enough.)

I restructured the code somewhat and turned it into a working example on the Go Playground. I make no promises as to suitability, etc.