Nested structs that are part of a mapping broken in Solidity 0.5.0?

Question

The following code compiled successfully with Soldity 0.4.21. With 0.5.0 it triggers a fatal compilation error as follows:

UnimplementedFeatureError: Encoding type "struct TestNestedStructInMapping.structNested memory" not yet implemented.
Compilation failed. See above.
Truffle v5.0.0-beta.2 (core: 5.0.0-beta.2)
Solidity v0.5.0 (solc-js)
Node v8.11.1

Here is the code:

pragma solidity ^0.5.0;

contract TestNestedStructInMapping {

    // The struct that is nested.
    struct structNested {
        uint dummy;
    }

    // The struct that holds the nested struct.
    struct structMain {
        structNested gamePaymentsSummary;
    }

    // The map that maps a game ID to a specific game.
    mapping(uint256 => structMain) public s_mapOfNestedStructs;
}

Here is a link to a Truffle project that you can pull and test with:

https://github.com/roschler/nested-structs-tests.git

Does anyone know how to solve this?

Answer 1

You can solve it by removing the word public from the mapping.

The storage structure itself is acceptable and can be expected to work. However, the "free" getter for such a structure is not implemented in the compiler.

It appears you are right about a breaking change, given that it compiles without complaint under 0.4.25. Possibly another kind soul will chime in with a precise answer about the limitation and where we go from here. In any case, I expect you should be able to carry on with your own explicit getter functions.

Hope it helps.