Understanding Delegate Calls in Smart Contract

Delegate calls in smart contract generally used to interact with other smart contract where Delegation is the one of the way. When a smart contract uses a delegate call to call a method, it executes and loads the method code from other smart contracts.

When a method executes by delegation call then the following values do not change

msg.sender

msg.value

address(this)

The smart contract that execute and loads the function of smart contract using delegate calls can write and read state variables and the smart contract that holds the methods is not subjected to writes or reads.

If Smart Contract A utilizes a deligate call to another Smart Contract B then the following statements will be true:

Smart Contract A state variables can be 'write and read'.

Smart Contract B state variables never 'write and read'.

Smart Contract B functions can be read and write the variables of both Smart Contract A and B.

Examples

Smart Contract A has the following things:

address(this) == 0x514910771AF9Ca656af840dff83E8264EcF986CA

State variable called “string tName” is “TestTokenA.”

External method ‘init()’ used to delegate call to Smart Contract B setTName(string calldata _newTName)’ method.

Smart Contract B has the following things:

address(this) == 0x95aD61b0a150d79219dCF64E1E6Cc01f0B64C4cE

State variable called “string tName” is “TestTokenB.”

external method ‘setTName(string calldata _newTName)’ that updates the ‘tName’ state variable to the ‘_newTName’.

When we call the ‘init()’ method in Smart Contract A with 1 ETH:

1. These values will be set:

address(this) == 0x514910771AF9Ca656af840dff83E8264EcF986CA

msg.sender == 0x868dae27Eb45B26835D69b15C525c8B73FF20e3B

msg.value == 1 ETH

2. When‘init()’ method calls the ’setTName’ method in Smart Contract B then these values are returned:

address(this) == 0x514910771AF9Ca656af840dff83E8264EcF986CA

msg.sender == 0x868dae27Eb45B26835D69b15C525c8B73FF20e3B

msg.value == 1 ETH

3. In Smart Contract A, the value of the ‘tName’ state variable is changes.

Conclusion

In this article, we have learned how to delegate calls in a smart contract from Contract A to B and how state variables and functions work.