EXTCODECOPY

EXTCODECOPY is an opcode in the Ethereum Virtual Machine (EVM) used to copy data from the code of another account. It is a low-level operation that allows smart contracts to access and retrieve bytecode from other deployed contracts. The opcode takes three arguments: the destination memory offset, the address of the source account, the starting offset within the source account's code, and the number of bytes to copy. The copied bytes are then placed into the contract's memory at the specified destination offset.

The primary use case for EXTCODECOPY is to inspect the code of other contracts. This can be useful for various purposes, such as verifying contract integrity, determining the presence of specific functions or data, or facilitating interoperability between contracts that need to understand each other's structure. For instance, a contract might use EXTCODECOPY to read a specific part of another contract's bytecode to check for a particular version or feature.

It's important to note that EXTCODECOPY only retrieves the raw bytecode of a contract. It does not interpret the code, call its functions, or access its storage. The operation is purely about data retrieval at the byte level. The gas cost associated with EXTCODECOPY is determined by the amount of data being copied, with a base cost plus an additional cost per byte. This makes it a relatively expensive operation, especially when copying large amounts of data, and developers should use it judiciously to manage gas consumption.