interfaces.jl

const _interfaces = Dict{Function,Vector{DataType}}()

function addInterface(d::DataType, f::Function...)
    for g in f
        if haskey(_interfaces, g)
            push!(_interfaces[g], d) 
        else
            _interfaces[g] = DataType[d]
        end
    end
end

function checkInterface(d::DataType)
    
    for (f,itypes) in _interfaces
    
        isInInterfaceTable = false
        local parentType
        for it in itypes
            if d <: it
                isInInterfaceTable = true
                parentType = it
            end
        end
        
        isInMethodTable = false
        
        if isInInterfaceTable
            mt = methods(f)
            for m in mt
                if d <: m.sig[1]
                    isInMethodTable = true
                end
            end
        end
        
        if isInInterfaceTable && !isInMethodTable
            error("Interface not implemented!\n $d has to implement ", string(f), " in order to be subtype of $parentType !")
        end
    end    
    
    return true
end