Batch

At the time of this writing, public/private key pair Ethereum accounts (EOAs) cannot directly perform multiple operations within a single transaction, except by invoking a smart contract that will do so on their behalf. The EVC exposes a batch function that allows multiple operations to be executed together. This has several advantages for users:

• Atomicity: The user knows that either all of the operations in a batch will execute, or none of them will, so there is no risk of being left with partial or inconsistent positions.
• Gas savings: If contracts are invoked multiple times, then the cost of "cold" access can be amortized across all of the invocations.
• Status check deferrals: Sometimes multiple operations in a batch may require status checks or it is more convenient or efficient to perform some operation that would leave an account/vault in an invalid state, but fix this state in a subsequent operation in a batch. For example, you may want to perform withdrawal and borrow in one batch or borrow and swap before you deposit your collateral. With batches, these checks can be performed once at the end of a batch (which can also itself be more gas efficient).

Same as call, batches can be composed of both calls to the EVC itself and external calls. Calling the EVC is how users can enable collateral from within a batch, for example. In order to preserve msg.sender, EVC self-calls are in fact done with delegatecall.

Batches will often be a mixture of external calls, some of which call vaults and some of which call other unrelated contracts. For example, a user might withdraw from one vault, then perform a swap on Uniswap, and then deposit into another vault. Each batch item specifies onBehalfOfAccount for which the authentication rules are the same as for call.