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## Simple Summary
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To simply and cheaply clone contract functionality in an immutable way, this standard specifies a minimal bytecode implementation that delegates all calls to a known, fixed address.
By standardizing on a known minimal bytecode redirect implementation, this standard allows users and third party tools (e.g. Etherscan) to (a) simply discover that a contract will always redirect in a known manner and (b) depend on the behavior of the code at the destination contract as the behavior of the redirecting contract. Specifically, tooling can interrogate the bytecode at a redirecting address to determine the location of the code that will run - and can depend on representations about that code (verified source, third-party audits, etc). This implementation forwards all calls and 100% of the gas to the implementation contract and then relays the return value back to the caller. In the case where the implementation reverts, the revert is passed back along with the payload data (for revert with message).
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This standard supports use-cases wherein it is desireable to clone exact contract functionality with a minimum of side effects (e.g. memory slot stomping) and with low gas cost deployment of duplicate proxies.
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The exact bytecode of the standard clone contract is this: `363d3d373d3d3d363d73bebebebebebebebebebebebebebebebebebebebe5af43d82803e903d91602b57fd5bf3` wherein the bytes at idices 10 - 29 (inclusive) are replaced with the 20 byte address of the master functionality contract.
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The goals of this effort have been the following:
- inexpensive deployment (low gas to deploy clones)
- support clone initialization in creation transaction (through factory contract model)
- simple clone bytecode to encourage directly bytecode interrogation (see CloneProbe.sol in the clone-factory project)
- dependable, locked-down behavior - this is not designed to handle upgradability, nor should it as the representation we are seeking is stronger.
- small operational overhead - adds a single call cost to each call
- handles error return bubbling for revert messages
## Backwards Compatibility
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There are no backwards compatibility issues. There may be some systems that are using earlier versions of the proxy contract bytecode. They will not be compliant with this standard.
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NOTE: as an effort to reduce gas costs as much as possible, the above bytecode depends on EIP-211 specification that `returndatasize` returns zero prior to any calls within the call-frame. `returndatasize` uses 1 less gas than `dup*`.
Proxy deployment can be further optimized by installing the master contract at a vanity contract deployment address with leading zero-bytes. By generating a master contract vanity address that includes Z leading 0 bytes in its address, you can shorten the proxy bytecode by replacing the `push20` opcode with `pushN` (where N is 20 - Z) followed by the N non-zero address bytes. The revert jump address is decremented by Z in this case. Here is an example where Z = 4:
