Почему нельзя вызвать через code переменная?

local code var = ... // ok
call var.execute() // Ошибка ругает
// или
call var.evaluate() // Тоже ошибка

/* -------------------------------------------------- */
    private function interface Use takes unit u, TypeItem ti returns nothing
    /* -------------------------------------------------- */
    private module TypeItemUse
        private Use e
        private static method onInit takes nothing returns nothing
            local trigger t = CreateTrigger()
            local integer i = 0
            
            loop
                call TriggerRegisterPlayerUnitEvent(t, Player(i), EVENT_PLAYER_UNIT_USE_ITEM, null)
                set i = i + 1
                exitwhen i == bj_MAX_PLAYER_SLOTS
            endloop
            
            call TriggerAddCondition(t, Condition(function thistype.onCall))
        endmethod

        private static method onCall takes nothing returns nothing
            local integer i = GetItemTypeId(GetManipulatedItem())
            local thistype this = thistype[thistype.getIndex(i)]
            
            if this.e != 0 then
                call this.e.evaluate(GetManipulatingUnit(), this)
            endif
        endmethod
        
        method addEventUse takes Use e returns nothing
            set this.e = e
        endmethod
    endmodule