Interfaces implementation visibility

Question

I have this interface:

pragma solidity ^0.4.24;
interface EventsInterface 
{
   function removeValueFromArray(uint _userId, uint[] array) external 
   returns(uint[]);
}

And this contract:

pragma solidity ^0.4.24;

import "./EventsInterface.sol";

contract EventsImpl is EventsInterface {

    function removeValueFromArray(uint _userId, uint[] _array) internal returns(uint[]) {

    uint[] storage auxArray;

    for (uint i = 0; i < _array.length; i++){
        if(_array[i] != _userId)
            auxArray.push(_array[i]);
    }

    return auxArray;
}
}

When I try to deploy de contract. Remix report me a error:

This contract does not implement all functions and thus cannot be created.

Changing to public the Impl function:

function removeValueFromArray(uint _userId, uint[] _array) public returns(uint[]) {

    uint[] storage auxArray;

    for (uint i = 0; i < _array.length; i++){
        if(_array[i] != _userId)
            auxArray.push(_array[i]);
    }

    return auxArray;
}

I get the following error

TypeError: Function overload clash during conversion to external types for arguments

To fix the issue I set to public bouth functions (Interface/Implementation) and works. But I getting one warning that tell me that interface function must be external and not public

Answer 1

Considering you actually need this function to be internal, you could use just inheritance instead of interface:

pragma solidity 0.4.24;

contract EventsInterface 
{
   function removeValueFromArray(uint _userId, uint[] memory _array) internal returns(uint[] memory);
}

contract EventsImpl is EventsInterface {
    uint[] baseArray;

    function removeValueFromArray(uint _userId, uint[] memory _array) internal returns(uint[] memory) {
        uint[] storage auxArray = baseArray;

        for (uint i = 0; i < _array.length; i++){
            if(_array[i] != _userId)
                auxArray.push(_array[i]);
        }

        return auxArray;
    }
}

This contract will compile with version 0.4.24 and with version 0.5.4, too.

Note that you must set the location of a few variables (namely the original array and the returned uint[]).