VectorPrisms -- a way of viewing any simple nested struct as a vector

vectorprism.jl

module VectorPrisms

function check_compatible(::Type{T}) where T
    isconcretetype(T) || error("Type is not fully concrete")
    for ft in fieldtypes(T)
        check_compatible(ft)
    end
end
check_compatible(::Type{<:Array}) = error("Type contains an array")
check_compatible(::Type{Nothing}) = error("Nothing is not supporting.")


"can subtype this to automatically be an AbstractVector"
abstract type AbstractVectorViewable{T} <: AbstractVector{T} end

"Can wuse this to wrap anything else to make it a AbstractVector"
struct PrismView{T, B} <: AbstractVectorViewable{T}
    backing::B
end
function PrismView(x::B) where B
    check_compatible(B)
    T = determine_eltype(B)
    return PrismView{T, B}(x)
end

function determine_eltype(::Type{B}) where B
    fieldcount(B) == 0 && return B
    eltype = Union{}
    for ft in fieldtypes(B)
        eltype = Union{eltype, determine_eltype(ft)}
    end
    return eltype
end


function Base.getindex(x::AbstractVectorViewable{T}, ii:Int) where T
    ind_remaining = ii
    function getsome(v::T)
        ind_remaining-=1
        if iszero(ind_remaining)
            return v
        else
            return nothing
        end
    end
    function getsome(v)
        for field_ind in 1:fieldcount(typeof(v))
            r = getsome(getfield(v, field_ind))
            isnothing(r) || return r
        end
        throw(BoundsError())
    end
    
    return getsome(x)
end
    
function Base.size(x::AbstractVectorViewable{T}) where T
    size_from(::Type{<:T}) = 1
    function size_from(::Type{V}) where V
        sum(fieldtypes(V)) do fieldtype
            size_from(fieldtype)
        end
    end
    return size_from(x)
end

# Note: this will error if the particular index does not line up with a mutable struct position
# This could be made more powerful using Accessors.jl
function Base.setindex!(x::AbstractVectorViewable{T}, value, ii:Int) where T
    ind_remaining = ii
    function setsome(v::T)
        ind_remaining-=1
        if iszero(ind_remaining)
            return true
        else
            return nothing
        end
    end
    function setsome(v)
        for field_ind in 1:fieldcount(typeof(v))
            set_this = setsome(getfield(v, field_ind))
            set_this && setfield(v, field_ind, s)
        end
        throw(BoundsError())
    end
    
    return setsome(x)
end

end  # module