Add a getter for an array of tokens held by an owner

[chebykin]

Problem

I want to inherit ERC721Full.sol contract and add an extra getter for an array of tokens held by a given user.

Expected behaviour

In previous versions it was possible by adding an extra function and accessing an internal _ownedTokens mapping:

function tokensOfOwner(address _owner) external view returns (uint256[]) {
    return ownedTokens[_owner];
}

Current behaviour

In version 2.x it is impossible to access a private _ownedTokens mapping.

[frangio]

I think we could add an internal function in ERC721Enumerable for this.

function _tokensOfOwner(address owner) internal view returns (uint256[] storage) {
    return _ownedTokens[owner];
}

[chebykin]

Thank you! Will wait for this feature.

[nventuro]

Isn't this a duplicate of #1102?

[frangio]

Hm, that issue is about an external interface, this one is about an internal one for extension purposes.

[Aniket-Engg]

shouldn't uint256[] storage be uint256[] memory?
@frangio Clear it, i will take this one.

[frangio]

@Aniket-Engg I think it should be storage because the function would be returning a pointer to the array that is held in storage. Copying the array to memory would be very expensive unnecessarily IMO.

[imsys]

For some reason this was removed on bd07784

[arzusa]

I think we could add an internal function in ERC721Enumerable for this.

function _tokensOfOwner(address owner) internal view returns (uint256[] storage) {
    return _ownedTokens[owner];
}

not work

TypeError: Return argument type mapping(uint256 => uint256) is not implicitly convertible to expected type (type of first return variable) uint256[] storage pointer.