Allow mapping to struct with dynamically-sized type to implement inherited function

[travs]

Overriding functions defined in interfaces with the automatically-generated getters from public state variables usually work great. This was reported in a previous issue (#3514) and fixed.

However, when the return type is a struct that has a dynamically-sized type, like the string in the example below, the generated getter doesn't override properly, causing a compiler error.

// sample.sol
pragma solidity 0.6.4;
pragma experimental ABIEncoderV2;

interface IA {
    struct Baz {
        address a;
        address b;
        string  c;
    }

    function bazMap(address) external returns (Baz memory);
}

contract A is IA {
    mapping (address => Baz) public override bazMap;
}

$ solc sample.sol  # it's version 0.6.4
Error: Overriding public state variable return types differ.
  --> sample.sol:15:5:
   |
15 |     mapping (address => Baz) public override bazMap;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Note: Overridden function is here:
  --> sample.sol:11:5:
   |
11 |     function bazMap(address) external returns (Baz memory);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Based on the docs, I might expect the function to override to be like:

function bazMap(address) external returns (address,address)

but that doesn't work either.

Related to: #6337, #3514, #7521, #4244

[ekpyron]

Thanks for reporting! I just confirmed this and will look into fixing it.

[ekpyron]

This should be "fixed" by #8491.
Once merged, in your example you could do:

pragma solidity 0.6.4;
pragma experimental ABIEncoderV2;

interface IA {
    struct Baz {
        address a;
        address b;
        string  c;
    }

    function bazMap(address) external returns (address, address, string memory);
}

contract A is IA {
    mapping (address => Baz) public override bazMap;
}

To change this to overriding returns (Baz memory) is tracked in #6337, but that's a breaking change unfortunately.

[chriseth]

I'm closing this.

[0xDEnYO]

Hey Guys,

I am still facing the same problem. Not sure if I am missing something.

Lets keep this example (though I am using solc 0.8.4):

pragma solidity 0.8.4;

interface IA {
    struct Baz {
        address a;
        address b;
        string  c;
    }

    function bazMap(address) external returns (address, address, string memory);
}

contract A is IA {
    mapping (address => Baz) public override bazMap;
}

If I do it this way and I access one member of bazMap. then its not possible to access member.a cause the compiler doesnt know that this member has this attribute. Even if I write:
function bazMap(address) external returns (address a, address b, string memory c);

Still not possible.

What am I missing?
Also the following approach to let the mapping return a type that is known in/by the interface doesnt work:

contract A is IA {
    mapping (address => IA.Baz) public override bazMap;
}

Compiler says return types differ. But they dont, they are exactly the same and get even referenced with their origin. Dont really understand how to implement this.

[chriseth]

Please ask this question either in ethereum stackexchange or the solidity channel on matrix - this issue is not the right place.
I also don't really understand what you want to achieve. Both your examples compile for me.

[cameel]

Here's a related issue that's still open: #11826.

@danielb1986 If you have a snippet that produces a compilation error and you think it's a bug (rather than just incorrect usage), you could post it there. Please use a complete example though - you said that accessing some members causes errors but I don't see that in your example and we're left guessing what might be happening.

If you're unsure, drop by at the #solidity channel so that we can discuss it first.