[Ethereum] Solidity return array from struct

solidity

I use solidity with web3.js and know that we actually cannot return the whole struct array, but I would like to know if it is possible to return only a type in the struct as an array.

Lets say i have the following struct:

struct aStruct {
    bytes8 a; 
    bytes8 b;
}

aStruct[10000] aStr;

Can I now make a function, where I return aStr.a, the whole "a" as an array?

Best Answer

I'm going to go out on a limb here and say you probably don't want to do that, even if you could, which you can't, at least for now.

The blockchain is not like other platforms. Some of the changes are hard to accept because they're opposite of what experience teaches.

Iteration over a set is almost always a client-side concern. It's easy to see how a client with the whole data set can figure that out on its own. You shouldn't burden the contract with a concern the clients can address without assistance.

This might help explain where I'm coming from. https://medium.com/p/2303010c8b09/

Update

Since 0.4.17 you can use pragma experimental ABIEncoderV2 to return structs. Of course, until the experimental keyword is removed, it's not safe to use it in production apps.

Solidity Return Struct – Creating and Using Data Structures

Update:

See here. We can return structs but only for internal calls.

Returning structs in new version in Solidity

In this snippet, function tryIt() returns true after a successful compile. It's just making an internal call (success). getAssetStructById() fails when called from outside.

pragma solidity 0.4.17;

contract Test {

    enum assetState{something}

    mapping(uint256 => asst) assetsById;

    struct asst {
        uint256 assetId;
        uint256 next;
        uint256 prev;
        uint256 timestampCreation;
        address assetOwner;
        address issuer;
        string content;
        uint256 sellPrice;
        assetState state;
    }

    function getAssetStructById(uint256 assetId) public view returns (asst _asset) {
        return (assetsById[assetId]);
    }

    function tryIt(uint id) public view returns(bool success) {
        asst memory a = getAssetStructById(id); 
        return true;
    }
}

Hope it helps.

Best Answer

Related Solutions

Solidity – How to Return Struct When Function is Called

Update

Solidity Return Struct – Creating and Using Data Structures

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