Add CleverDicts as submodule to MOI.Utilities

Project.toml

@@ -5,9 +5,10 @@ version = "0.9.0"
 [deps]
 BenchmarkTools = "6e4b80f9-dd63-53aa-95a3-0cdb28fa8baf"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
+OrderedCollections = "bac558e1-5e72-5ebc-8fee-abe8a469f55d"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
-Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 
 [compat]
 julia = "1"

src/Utilities/CleverDicts.jl

@@ -0,0 +1,217 @@
+module CleverDicts
+
+import OrderedCollections
+
+"""
+    CleverDict{K, V}
+
+A smart storage type for managing sequential objects with non-decreasing integer
+indices.
+
+Provided no keys are deleted, the backing storage is a `Vector{V}`. Once a key
+has been deleted, the backing storage switches to an `OrderedDict{K, V}`.
+
+The i'th ordered element can be obtained with `c[LinearIndex(i)]`.
+
+Note that querying a `LinearIndex` immediately after deleting a key via
+`delete!` is very slow. (It requires a rebuild of an ordered list of variables.)
+
+Store an item `val` using `add_item(c::CleverDict, val)`. `add_item` returns a
+key corresponding to the stored item.
+
+Overload the functions `index_to_key` and `key_to_index` to enable mappings
+between the integer index of the vector and the dictionary key.
+
+## Example
+
+```julia
+struct MyKey
+    x::Int
+end
+index_to_key(::Type{MyKey}, i::Int) = MyKey(i)
+key_to_index(key::MyKey) = key.x
+```
+"""
+mutable struct CleverDict{K, V}
+    last_index::Int
+    vector::Union{Nothing, Vector{V}}
+    dict::Union{Nothing, OrderedCollections.OrderedDict{K, V}}
+    CleverDict{K, V}() where {K, V} = new{K, V}(0, V[], nothing)
+end
+
+"""
+    index_to_key(::Type{K}, index::Int)
+
+Create a new key associated with the integer value `index`.
+"""
+function index_to_key end
+
+"""
+    key_to_index(key::K)
+
+Map `key` to an integer valued index, assuming that there have been no
+deletions.
+"""
+function key_to_index end
+
+"""
+    add_item(c::CleverDict{K, V}, val::Val)::K where {K, V}
+
+Set `val` in the next available key, and return that key.
+"""
+function add_item(c::CleverDict{K, V}, val::V)::K where {K, V}
+    c.last_index += 1
+    key = index_to_key(K, c.last_index)
+    if c.dict === nothing
+        push!(c.vector, val)
+    else
+        c.dict[key] = val
+        # If there is a vector (e.g., because it has been rebuild for
+        # `LinearIndex`), clear it.
+        c.vector = nothing
+    end
+    return key
+end
+
+function Base.empty!(c::CleverDict{K, V})::Nothing where {K, V}
+    c.vector = V[]
+    c.last_index = 0
+    c.dict = nothing
+    return
+end
+
+function Base.getindex(c::CleverDict{K, V}, key::K)::V where {K, V}
+    # Perform this `haskey` check up front to detect getting with keys that are
+    # invalid (i.e., have previously been deleted).
+    if !haskey(c, key)
+        throw(KeyError(key))
+    end
+    # Case  I) no call to `Base.delete!`, so return the element:
+    # Case II) `Base.delete!` must have been called, so return the element
+    #          from the dictionary.
+    return c.dict === nothing ? c.vector[key_to_index(key)] : c.dict[key]
+end
+
+function Base.setindex!(c::CleverDict{K, V}, val::V, key::K)::V where {K, V}
+    # Perform this `haskey` check up front to detect setting with keys that are
+    # invalid (i.e., have already been deleted). You can only call setindex!
+    # with a key obtained from `new_key` that hasn't been deleted.
+    if !haskey(c, key)
+        throw(KeyError(key))
+    elseif c.dict === nothing
+        @assert c.vector !== nothing
+        c.vector[key_to_index(key)] = val
+    else
+        c.dict[key] = val
+    end
+    return val
+end
+
+struct LinearIndex
+    i::Int
+end
+
+function Base.getindex(c::CleverDict{K, V}, index::LinearIndex)::V where {K, V}
+    if !(1 <= index.i <= length(c))
+        throw(KeyError(index))
+    end
+    # Get the `index` linear element. If `c.vector` is currently `nothing`
+    # (i.e., there has been a deletion), rebuild `c.vector`. This is a
+    # trade-off: We could ensure `c.vector` is always updated, but this requires
+    # a `splice!` in `delete!`, making deletions costly. However, it makes this
+    # `getindex` operation trival because we would never have to rebuild the
+    # vector.
+    # The current implemented approach offers quick deletions, but an expensive
+    # rebuild the first time you query a `LinearIndex` after a deletion or a new
+    # key is added. Once the rebuild is done, there are quick queries until the
+    # next deletion or addition. Thus, the worst-case is a user repeatedly
+    # deleting a key and then querying a LinearIndex (e.g., getting the MOI
+    # objective function).
+    if c.vector === nothing
+        c.vector = Vector{V}(undef, length(c))
+        for (i, val) in enumerate(values(c.dict))
+            c.vector[i] = val
+        end
+    end
+    return c.vector[index.i]::V
+end
+
+function Base.delete!(c::CleverDict{K, V}, key::K)::Nothing where {K, V}
+    if c.dict === nothing
+        c.dict = OrderedCollections.OrderedDict{K, Union{Nothing, V}}()
+        for (i, info) in enumerate(c.vector)
+            c.dict[index_to_key(K, i)] = info
+        end
+    end
+    delete!(c.dict, key)
+    c.vector = nothing
+    return
+end
+
+function Base.length(c::CleverDict)::Int
+    return c.dict == nothing ? length(c.vector) : length(c.dict)
+end
+
+function Base.isempty(c::CleverDict)
+    return c.dict !== nothing ? isempty(c.dict) : length(c.vector) == 0
+end
+
+Base.haskey(::CleverDict, key) = false
+function Base.haskey(c::CleverDict{K, V}, key::K)::Bool where {K, V}
+    if c.dict === nothing
+        return 1 <= key_to_index(key) <= length(c.vector)
+    else
+        return haskey(c.dict, key)
+    end
+end
+
+# Here, we implement the iterate functions for our `CleverDict`. If the backing
+# datastructure is an `OrderedDict`, we just forward `iterate` to the dict. If
+# it's the vector, we create a key-value pair so that `iterate` returns the same
+# type regardless of the backing datastructure. To help inference, we annotate
+# the return type.
+#
+# Also note that iterating an `OrderedDict` returns an `Int` state variable.
+# This is identical to the type of the state variable that we return when
+# iterating the vector, so we can add a type restriction on
+# `iterate(c, s::Int)`.
+
+function Base.iterate(
+    c::CleverDict{K, V}
+)::Union{Nothing, Tuple{Pair{K, V}, Int}} where {K, V}
+    if c.dict !== nothing
+        return iterate(c.dict)
+    else
+        @assert c.vector !== nothing
+        if length(c.vector) == 0
+            return nothing
+        end
+        key = index_to_key(K, 1)
+        return key => c.vector[1], 2
+    end
+end
+
+function Base.iterate(
+    c::CleverDict{K, V}, s::Int
+)::Union{Nothing, Tuple{Pair{K, V}, Int}} where {K, V}
+    if c.dict !== nothing
+        return iterate(c.dict, s)
+    else
+        @assert c.vector !== nothing
+        if s > length(c.vector)
+            return nothing
+        end
+        key = index_to_key(K, s)
+        return key => c.vector[s], s + 1
+    end
+end
+
+function Base.values(c::CleverDict{K, V}) where {K, V}
+    return c.dict !== nothing ? values(c.dict) : c.vector
+end
+
+function Base.keys(c::CleverDict{K, V}) where {K, V}
+    return c.dict !== nothing ? keys(c.dict) : index_to_key.(K, 1:length(c))
+end
+
+end

src/Utilities/Utilities.jl

@@ -29,4 +29,6 @@ include("mockoptimizer.jl")
 include("cachingoptimizer.jl")
 include("universalfallback.jl")
 
+include("CleverDicts.jl")
+
 end # module