Lists example

lists.sol

pragma solidity ^0.6.0;

contract Lists {
    mapping(uint => uint[]) public list;
    
    function add(uint id, uint value)
        public
    {
        list[id].push(value);
    }
    
    function get(uint id, uint index)
        public
        view
        returns(uint)
    {
        return list[id][index];
    }
    
    function count(uint id)
        public
        view
        returns(uint)
    {
        return list[id].length;
    }
    
    function sliceItems(uint id, uint offset, uint limit)
        public
        view
        returns(uint[] memory)
    {
        uint diff = limit - offset;
        uint[] memory result = new uint[](diff);
        for (uint i = 0; i < diff; i++) {
            result[i] = list[id][offset + i];
        }
        return result;
    }
    
    function callSlice(uint id)
        public
        view
        returns (uint[] memory)
    {
        uint length = count(id);
        
        return sliceItems(id, 0, length);
    }
    
    function callList(uint id)
        public
        view
        returns (uint[] memory)
    {
        uint length = count(id);
        uint[] memory result = new uint[](length);
        
        for (uint i = 0; i < length; i++) {
            result[i] = get(id, i);
        }
        
        return result;
    }
}

contract RemoteList {
    Lists public remote;
    
    constructor(address _remote) public {
        require(_remote != address(0), 'remote_exists');
        remote = Lists(_remote);
    }
    
    function callSlice(uint id)
        public
        view
        returns(uint[] memory)
    {
        uint length = remote.count(id);
    
        return remote.sliceItems(id, 0, length);
    }
    
    function callList(uint id)
        public
        view
        returns(uint[] memory)
    {
        uint length = remote.count(id);
        uint[] memory result = new uint[](length);
        
        for (uint i = 0; i < length; i++) {
            result[i] = remote.get(id, i);
        }
        
        return result;
    }
}