Is it possible to create multiple anonymous proxies in the same transaction?

Question

I guess I have to make use of the utility.batch call but I am not sure how to pass the different anonymous proxy TXs in the batch call. I am also not sure of the use of the variable index in the anonymous call. Maybe it is there to distinguish the different anonymous proxy transactions?

Answer 1

The reason for the index in the anonymous call in pallet-proxy is exactly for the purposes of disambiguating multiple anonymous proxies in a single transaction.

It's because of the way that the proxies module deterministically generates account IDs for proxies: https://github.com/paritytech/substrate/blob/f98ef8abfc54bb7801b21be899e63f5058350e14/frame/proxy/src/lib.rs#L648-L664

    pub fn anonymous_account(
        who: &T::AccountId,
        proxy_type: &T::ProxyType,
        index: u16,
        maybe_when: Option<(T::BlockNumber, u32)>,
    ) -> T::AccountId {
        let (height, ext_index) = maybe_when.unwrap_or_else(|| {
            (
                system::Pallet::<T>::block_number(),
                system::Pallet::<T>::extrinsic_index().unwrap_or_default(),
            )
        });
        let entropy = (b"modlpy/proxy____", who, height, ext_index, proxy_type, index)
            .using_encoded(blake2_256);
        Decode::decode(&mut TrailingZeroInput::new(entropy.as_ref()))
            .expect("infinite length input; no invalid inputs for type; qed")
    }

As you can see, it takes the block height and current extrinsic index within the block as inputs. If this isn't within a batch call, then there's no need for disambiguation. However, if multiple calls to anonymous_account occur within the same extrinsic, they need a disambiguating input to the account ID generation function.

https://github.com/paritytech/substrate/blob/f98ef8abfc54bb7801b21be899e63f5058350e14/frame/proxy/src/lib.rs#L317

        pub fn anonymous(
            origin: OriginFor<T>,
            proxy_type: T::ProxyType,
            delay: T::BlockNumber,
            index: u16,
        ) -> DispatchResult {
            let who = ensure_signed(origin)?;

            let anonymous = Self::anonymous_account(&who, &proxy_type, index, None);

        // .. remainder omitted
        }

This is why fn anonymous accepts an index the user can use to avoid collisions in a batch.