Account abstraction is a paradigm for chains where assets are held by smart contracts exclusively, not EOAs.

As such, any kind of account contract can be coded; your question may have as many answers as there are account contracts implementation!
1. You can not recover a properly generated key if you lose it. However, your smart contract can implement some specific logic in case you lose it. EG "if this key doesn't interact for 1 month, let this other key take over"
2. If you find a way to authenticate the user safely without using a key, you can implement it. You can also have communal wallets where anyone can perform any action
3. Yes

There are a bunch of questions about key storage in a new "Account Abstraction" paradigm.
1. Can I recover my key if I lose it?
2. Can I have a key-less wallet?
3. Can I easily create new wallets like in Metamask "Add Account" with only 1 seed phrase?
---

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How will work an account abstaction wallet with the key?

How do I connect my wallet to my Pathfinder node?

Hello, Do I understand this correctly: Pathfinder JSON-RPC V0.1.0 does not support InvokeTXNV1 yet, right? At least, I do not `nonce` in `add_invoke_transaction`.

Do you plan to add it in JSON-RPC V0.1.0 like devnet (not being compliant to the spec) or will you introduce it with JSON-RPC V0.2.0?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Can anyone explain Pathfinder JSON-RPC InvokeTXNV1?

Hi, is there no way for me to have a struct as a `@storage_var` if it contains an array fo felts inside ?

For e.g. if I have a struct User:
```
struct User{
  values_len: felt ,
  VALUES: felt*,
}
```

Then I need to store a mapping from User Id to Users, is it not possible ?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

Is there no way for me to have a struct as a `@storage_var` if it contains an array fo felts inside ?

 I usually use truffle and solc is installed locally but not globally. Should I installed it? Is it worth adding in the readme?

 How do I check that my Solidity compiler version is >= 0.8.0 ?

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

e.g. in Solidity you can do
```solidity
mapping(address => mapping(uint256 => bool));
```
is this doable in Cairo? I want to do something similar to

```cairo

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 

```cairo
// 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
```cairo
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](https://www.newton.so/view?tags=discord)_

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

Hello! This is day 4 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Variables”. Can you launch this code with the instructions and write down how many steps the program has in the output?

[BONUS]: try to make it faster

```
// The following code outputs the 9th power of 2.
// 1. Click on "Debug" to run the code, and then click on
//    the arrows in the memory panel to trace the program
//    step by step.
//
// Observe that the computation of `z` take 8 steps and
// creates 8 temporary variables. This is because `let`
// simply replaces each instance of `y` with `x * x * x`
// and each instance of `z` with `y * y * y`, which is
// expanded to nine multiplications.
//
// 2. Change the two `let`s to `tempvar`s and run the program.
//
// "tempvar" stands for "temporary variable", which means that
// a variable will be allocated for the intermediate values
// (`x * x * x` and `y * y * y`). This reduces the same
// computation to use only 4 steps and 2 new variables.
//
// 3. Replace all three instance of the keyword `tempvar`
//    with `local`, uncomment the line containing `alloc_locals`
//    and run the code again.
//
// The behavior of the code doesn't change. This is because
// the keyword `local` allocates a new variables for the
// intermediate values as well. The main difference between
// `local` and `tempvar` is explained in the next challenge.

// Use the output builtin.
%builtins output

// Import the serialize_word() function.
from starkware.cairo.common.serialize import serialize_word

// Outputs the value 2^9.
func main{output_ptr: felt*}() {
    // alloc_locals;
    tempvar x = 2;
    let y = x * x * x;
    let z = y * y * y;
    // Because of the `let`s, the following line is equivalent to
    // serialize_word(x * x * x * x * x * x * x * x * x).
    serialize_word(z);
    return ();
}
```

---

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> 

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What is the difference between tempvar/let in Cairo Lang? How to use allow_locals and local?

Can tempvar be of a different type, say U256?

let's say

`tempvar foo: U256 = bar;` and bar being a U256?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

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How will work an account abstaction wallet with the key?

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