imm.jl

using MacroTools: @forward

struct Imm{T,N} <: AbstractArray{T,N}
	data::AbstractArray{T,N}
	optinds::Dict{T,T}
	iscommited::Ref{Bool}
end

# struct IsCommitted end
# struct IsNotCommitted end

# iscommited(arr::Imm{<:Any,<:Any, ::Base.RefValue{true}}) = IsCommitted()
# iscommited(arr::Imm{<:Any,<:Any, ::Base.RefValue{false}}) = IsNotCommitted()

iscommited(arr::Imm) = arr.iscommited[]

@forward Imm.data Base.show, Base.size

Imm(arr::AbstractArray{T,N}) where {T,N} = Imm(arr, Dict{T,T}(), Ref(true))
Imm(arr::Imm) = Imm(arr.data, Dict{T,T}(), Ref(true))

Base.IndexStyle(::Type{<:Imm}) = IndexLinear()
function Base.getindex(arr::Imm, i::Int)
	if iscommited(arr)
		arr.data[i]
	else
		haskey(arr.optinds, i) && return arr.optinds[i]
		arr.data[i]
	end
end

# getindex(arr::Imm, i::Int) = _getindex(arr, i, iscommited(arr))
# _getindex(arr::Imm, i, ::IsCommitted) = Base.getindex(arr.data, i)
# function _getindex(arr::Imm, i, ::IsNotCommitted)
# 	haskey(arr.optinds, i) && return arr.optinds[i]
# 	arr.data[i]
# end

Base.similar(arr::Imm) = Imm(similar(arr.data))
Base.setindex!(arr::Imm, val, ind) = (arr.iscommited[] = false; arr.optinds[ind] = val)
Base.setindex(arr::Imm, val, ind) = (arr.iscommited[] = false; arr.optinds[ind] = val)

function commit!(arr)
	for (k,v) in arr.optinds
		arr.data[k] = v
	end
	Imm(arr)
end

function Base.getindex(arr::Imm, i::Union{Base.UnitRange, Base.OneTo})
	makeopts!(arr)
	arr.data[i]
end