Are you able to nest mappings in Cairo like you can in Solidity?

Are you able to nest mappings in Cairo like you can in Solidity?

e.g. in Solidity you can do

mapping(address => mapping(uint256 => bool));

is this doable in Cairo? I want to do something similar to

func mappingA(value: felt) -> func mappingB(value: felt)  -> (value: felt){
}

mapping(x, y) -> (z) is not gonna work, here is some context:

I'm working through the sample ERC721_Metadata.cairo and ERC721_Metadata_Base contract shown here https://github.com/starknet-edu/starknet-erc721/tree/main/contracts/token/ERC721

It looks like from what I can tell the tokenUri is set for each domain, and even though calling the @view function does take in a tokenId, calling to set the tokenUri does not and it's not clear to me how that mapping could exist otherwise. So I wanted to modify the contract to have a token_id -> token_uri mapping. Because of the way those mappings exist though, you need to provide both the token_uri_len: felt and token_uri: felt* when writing them. This means it can only be done once, otherwise you'd need a specific @storage_var for every token that's minted, just to hold it's tokenuri. I was hoping to do something like

// Represents a tokenUri
struct TokenUri {
    // The length of the token bytes
    token_uri_len: felt,
    // The pointer to the beginning of the token uri bytes
    token_uri: felt*,
}

@storage_var
func token_uris(token_id: felt) -> (token_uri: TokenUri) {
}

But because of the token_url: felt* pointer in that struct, it can't be used as a storage variable return type. It gives an error when I try to compile showing

starknet_contracts/ERC721_Metadata.cairo:29:36: The return type of storage variables must be a felts-only type (cannot contain pointers).
func token_uris(token_id: felt) -> (token_uri: TokenUri) {

This question was originally posted on StarkNet Discord