CachedDicts

Attach a cache to your AbstractDict.

Usage

using CachedDicts
d = CachedDicts(cache, storage)::AbstractDict

Here cache and storage can be arbitrary AbstractDict{K,V}. Where reading from storage is slow (e.g. disk lookup) and reading from cache is fast.

Example

using CachedDicts
using LRUCache

mutable struct SlowDict <: AbstractDict{String, Int}
    dict::Dict{String,Int}
    nslow_calls::Int
end
SlowDict() = SlowDict(Dict{String,Int}(), 0)
for f in [:length, :get, :setindex!, :iterate, :delete!, :empty!]
    @eval (Base.$f)(d::SlowDict, args...) = $(f)(d.dict, args...)
end
function Base.getindex(o::SlowDict, key)
    # slow
    sleep(1e-2)
    o.nslow_calls += 1
    o.dict[key]
end

d_slow = SlowDict()
d_slow["1"] = 1
d_slow["2"] = 2

d_slow["1"]
@assert d_slow.nslow_calls == 1
d_slow["1"]
@assert d_slow.nslow_calls == 2
d_slow["1"]
@assert d_slow.nslow_calls == 3

cache = LRU{String,Int}(maxsize=2)
d = CachedDict(cache, d_slow)
@assert d_slow.nslow_calls == 3
d["1"]
# subsequent calls are cached
@assert d_slow.nslow_calls == 4
d["1"]
@assert d_slow.nslow_calls == 4
d["1"]
@assert d_slow.nslow_calls == 4