calldata

Calldata is a data location in Solidity that refers to the function call data passed to an external function. It is a read-only, non-persistent region that exists only for the duration of the call and contains the ABI-encoded arguments of that call. Calldata is intended for inputs, not for storage.

Calldata is cheaper than memory for external inputs because it avoids copying data. Accessing elements of calldata does not allocate memory; however, it is immutable within the function. If the function needs to modify the values, the data must first be copied into memory or another storage location.

Usage: You typically declare external functions with reference types (such as strings or arrays) marked as calldata to avoid copies, for example: function batchTransfer(address recipient, uint[] calldata amounts) external; In internal or public calls, data are usually handled in memory, and changes require copying.

Calldata contains the input data for the call: the function selector (the first four bytes) plus the ABI-encoded arguments. It differs from memory (modifiable) and storage (persistent) and is most useful when inputs are large or numerous.