Minimal proxy (clone) pattern in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Minimal Proxy (Clone) Pattern in blockchain?

It is a design pattern that creates lightweight contract copies by delegating calls to a single implementation contract, saving gas and deployment costs.

beginner

How does the Minimal Proxy pattern save gas?

By deploying very small proxy contracts that forward calls to a shared logic contract, it avoids duplicating code and reduces deployment size and cost.

intermediate

What opcode is commonly used in Minimal Proxy contracts to delegate calls?

The DELEGATECALL opcode is used to forward calls to the implementation contract while preserving the caller's context.

advanced

Show the basic bytecode structure of a Minimal Proxy contract.

It consists of a small piece of bytecode that includes a fixed prefix, the address of the implementation contract, and a fixed suffix that performs the delegatecall.

beginner

Why is the Minimal Proxy pattern also called the 'clone' pattern?

Because it creates clones of a contract that share the same logic but have separate storage, acting like lightweight copies.

What is the main benefit of using the Minimal Proxy pattern?

A Improved contract security

B Automatic contract upgrades

C Faster transaction execution

D Lower gas costs for deploying multiple contracts

Minimal Proxy contracts reduce deployment costs by sharing code, lowering gas fees.

Which opcode does a Minimal Proxy contract use to forward calls?

A STATICCALL

B CALL

C DELEGATECALL

D CREATE

DELEGATECALL forwards calls preserving the caller's context, essential for proxies.

In the Minimal Proxy pattern, where is the logic code stored?

A In a single implementation contract

B In each proxy contract

C On the client side

D In the blockchain's state root

The implementation contract holds the logic; proxies delegate calls to it.

What does a Minimal Proxy contract NOT have?

A Its own storage

B Its own logic code

C An address

D A delegatecall instruction

Minimal proxies do not contain logic code; they delegate to the implementation.

Why might developers choose the Minimal Proxy pattern?

A To reduce contract deployment costs

B To increase contract size

C To avoid using delegatecall

D To store all data on-chain

It reduces deployment costs by reusing logic code across many proxies.

Explain how the Minimal Proxy pattern works and why it is useful in blockchain development.

Think about how many contracts can share one logic contract to save costs.

Describe the role of DELEGATECALL in the Minimal Proxy pattern.

Focus on how calls are forwarded without changing the caller.

Practice

1. What is the main purpose of the Minimal proxy (clone) pattern in blockchain development?

easy

A. To replace the original contract with a new one

B. To increase the size of deployed contracts

C. To create cheap copies of contracts by forwarding calls

D. To store large amounts of data on-chain

Solution

1. Step 1: Understand the pattern's goal

   The minimal proxy pattern is designed to save gas and storage by creating lightweight copies of a contract.

2. Step 2: Identify the correct purpose

   It achieves this by forwarding calls to the original contract instead of duplicating all code.

3. Final Answer:

   To create cheap copies of contracts by forwarding calls -> Option C

4. Quick Check:

   Minimal proxy pattern = cheap contract copies [OK]

Hint: Minimal proxy means cheap clones forwarding calls [OK]

Common Mistakes:

• Thinking it increases contract size
• Confusing it with data storage methods
• Assuming it replaces original contracts

2. Which of the following Solidity code snippets correctly declares a minimal proxy clone using the create opcode?

easy

A. address clone = create(0, bytecode, bytecode.length);

B. address clone = new Contract();

C. address clone = create2(0, bytecode, bytecode.length);

D. address clone = delegatecall(bytecode);

Solution

1. Step 1: Identify the correct opcode for minimal proxy creation

   The create opcode is used to deploy a new contract with given bytecode.

2. Step 2: Match the syntax

   The syntax create(0, bytecode, bytecode.length) correctly uses create with zero value and bytecode parameters.

3. Final Answer:

   address clone = create(0, bytecode, bytecode.length); -> Option A

4. Quick Check:

   Minimal proxy uses create opcode like address clone = create(0, bytecode, bytecode.length); [OK]

Hint: Minimal proxy uses create, not new or delegatecall [OK]

Common Mistakes:

• Using new keyword which deploys full contract
• Confusing create2 with create
• Using delegatecall which does not deploy

3. Given the following Solidity code snippet for deploying a minimal proxy clone, what will be the output of clone.owner() if the original contract's owner is set to address 0x1234...?

address clone = Clones.clone(original);
// original.owner() returns 0x1234...
// clone forwards calls to original

medium

A. 0x1234... (same owner as original)

B. 0x0000... (zero address)

C. Revert error due to missing owner variable

D. Address of the clone contract

Solution

1. Step 1: Understand call forwarding in minimal proxy

   The clone forwards calls to the original contract, but storage is separate, so state variables like owner are not shared.

2. Step 2: Determine owner value returned

   Since owner() reads from the clone's storage which is uninitialized, it returns 0x0000... (zero address).

3. Final Answer:

   0x0000... (zero address) -> Option B

4. Quick Check:

   Clone forwards calls but has separate storage, owner = zero address [OK]

Hint: Clone has separate storage, owner defaults to zero [OK]

Common Mistakes:

• Assuming clone shares storage with original
• Expecting original owner to be returned
• Thinking clone address is returned

4. Identify the error in this minimal proxy deployment code snippet:

function clone(address implementation) external returns (address instance) {
    bytes20 targetBytes = bytes20(implementation);
    assembly {
        let clone_code := mload(0x40)
        mstore(clone_code, 0x3d602d80600a3d3981f3)
        mstore(add(clone_code, 0x14), targetBytes)
        instance := create(0, clone_code, 0x37)
    }
    require(instance != address(0), "Create failed");
}

medium

A. No error, code is correct

B. Missing delegatecall opcode in assembly

C. Using bytes20 instead of bytes32 for target address

D. Incorrect length passed to create (0x37 instead of 0x2d)

Solution

1. Step 1: Check the length parameter for create

   The minimal proxy bytecode length is typically 0x2d (45 bytes), but 0x37 (55 bytes) is passed incorrectly.

2. Step 2: Understand impact of wrong length

   Passing wrong length causes deployment of invalid bytecode, leading to failure or unexpected behavior.

3. Final Answer:

   Incorrect length passed to create (0x37 instead of 0x2d) -> Option D

4. Quick Check:

   Create length must match bytecode size [OK]

Hint: Check create length matches bytecode size [OK]

Common Mistakes:

• Ignoring bytecode length mismatch
• Confusing bytes20 and bytes32 usage
• Assuming delegatecall needed in deployment

5. You want to deploy 1000 instances of a contract cheaply using the minimal proxy pattern. Which approach best reduces gas and storage costs while allowing each clone to have its own owner?

hard

A. Use minimal proxies forwarding to one implementation and store owner in each clone's storage

B. Deploy 1000 full contracts separately with unique owners

C. Use minimal proxies forwarding to one implementation and store owner in the implementation contract

D. Deploy one contract and share the same owner for all clones

Solution

1. Step 1: Understand minimal proxy benefits

   Minimal proxies save gas by sharing code but have separate storage for each clone.

2. Step 2: Assign unique owners per clone

   Storing owner in each clone's storage allows unique ownership while sharing logic.

3. Step 3: Evaluate options

   Use minimal proxies forwarding to one implementation and store owner in each clone's storage uses minimal proxies with per-clone storage, reducing gas and allowing unique owners.

4. Final Answer:

   Use minimal proxies forwarding to one implementation and store owner in each clone's storage -> Option A

5. Quick Check:

   Minimal proxy + per-clone storage = cheap unique owners [OK]

Hint: Store owner in clone storage, share code via proxy [OK]

Common Mistakes:

• Storing owner only in implementation (shared state)
• Deploying full contracts wastes gas
• Sharing one owner for all clones