[Ethereum] TypeError: This type is only supported in the new experimental ABI encoder

remixsolidity

I am practicing my Solidity skills and while I did expect to get an error, I did not expect this error

TypeError: This type is only supported in the new experimental ABI
encoder. Use "pragma experimental ABIEncoderV2;" to enable the
feature. function getArray() public view returns (string[]) {

This is my code in Remix:

pragma solidity ^0.4.17;

contract Test {
    string[] public myArray;

    function Test() public {
        myArray.push("hola");
    }

    function getArray() public view returns (string[]) {
        return myArray;
    }
}

What gives here?

Is this because the standard ABI does not support dynamic nested arrays?

Best Answer

The error message you are seeing is a result of the fact that Solidity does not yet support two levels of dynamic arrays, which a string[] would be:

Is it possible to return an array of strings (string[]) from a Solidity function?

Not yet, as this requires two levels of dynamic arrays (string is a dynamic array itself).

The error is telling you to add an additional line to the top of your code:

pragma experimental ABIEncoderV2;

This feature came in Solidity version 0.4.19, which states:

Code Generator: New ABI decoder which supports structs and arbitrarily nested arrays and checks input size (activate using pragma experimental ABIEncoderV2;).

Note that in this case it does support nested arrays. I assume these features will eventually make their way into the production builds of Solidity, but it is not clear to me when. I tested, and your code does work when I add this additional pragma in remix.

Related Solutions

[Ethereum] Returning structs in new version in Solidity

Yes we can return structs.

But only in internal function calls.

pragma solidity ^0.4.19;

contract tester{

struct Person
{
    string name;
    uint age;
}

function getSome() public returns (Person a)
{
    Person memory p;
    p.name = "kashish";
    p.age =20;
    return p;
}

function wantSome() public returns (string,uint)
{
     Person memory p2 =getSome();
     return (p2.name,p2.age); // return multiple values like this
}
}

[Ethereum] This type is only supported in the new experimental ABI encoder – why

The standard ABI doesn't support structs. You can return the members of a struct in a fixed-length normally deliminated interface. For example:

function getter(bytes32 key) public returns(byte32 name, uint amount, bool isValid) :

return(myStruct[key].name, myStruct[key].amount, myStruct[key].isValid);

The idea of returning the struct object is experimental, e.g.

return(myStruct[key]);

Also, your snippet doesn't include the whole thing, but I suspect the issuerIndex is a list of keys, not the actual object. Your interface says it returns the object (the experimental feature) but possibly what you meant was returns(bytes32 key) which would be okay.

Hope it helps.

UPDATE

Based on comment below, the issue is the return value is cast as type "Issuer" which would be the experimental struct object. It should be cast as type address.

To return the address of the Issuer from the mapping:

returns(address issuer) { ...

return issuersIndex[index];

Best Answer

Related Solutions

[Ethereum] Returning structs in new version in Solidity

[Ethereum] This type is only supported in the new experimental ABI encoder – why

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