Contract Using An Interface Is Not Compiling

Question

I am learning Solidity and I am using Remix to experiment and enhance my learning. I am currently trying to create a simple contract that uses an Interface.

pragma solidity ^0.4.19;

contract InterfaceWithMe {

    function call() returns (string);

}

contract Interfacing {

    address ckAddress = 0x9fe1c58215407d67719ba680360940056e5eceb7;
    InterfaceWithMe daContract = InterfaceWithMe(ckAddress);

    function call() returns (string) {
        return daContract.call();
    }

When I try an compile this on Remix, I get the following type error on line 14:

TypeError:Return argument type inaccessible dynamic type is not implicitely convertibel to expected type (type of first return variable) string memory.

Here is the other contract that I use to interface with this contract:

pragma solidity ^0.4.19;

contract InterfaceWithMe {

    function call() returns (string) {
        return "Hello";
    }
}

Thanks for the help.

Answer 1

A fair bit of fiddling for readability and style.

pragma solidity 0.4.25;

contract Interface {
    function call() public pure returns (string);
    function isInterface() public pure returns(bool);
}

contract Interfacing {

    Interface daContract; 

    constructor(address theContract) public {
        daContract = Interface(theContract);
        require(daContract.isInterface());
    }

    function call() public view returns (string) {
        return daContract.call();
    }

}

contract InterfaceWithMe is Interface {

    function call() public pure returns (string) {
        return "Hello";
    }

    function isInterface() public pure returns(bool) {
        return true;
    }
}

Here it is in Remix to show it working.

1. Deploy InterfaceWithMe
2. Copy the deployed address to the clipboard.
3. Deploy Interfacing passing the address from the clipboard into the constructor.
4. Call call in `Interfacing.
5. Hello

Hope it helps.