How to call other smart contracts in a smart contract

Smart contract is a key function in blockchain technology, which allows developers to write codes to automatically perform a series of operations, thereby realizing various complex business logic. In many application scenarios, a smart contract may need to call another smart contract to complete certain tasks. This article will introduce how smart contracts call other smart contracts, and provide some examples to help readers better understand the process.

What is a smart contract?

Before discussing how to call other smart contracts, we need to understand what a smart contract is. A smart contract is a program running on a blockchain network that automates specific tasks. Smart contracts are commonly used to execute transactions of digital assets, manage ownership and control of digital assets, and monitor transaction activity in the network. Smart contracts use code to describe their behavior and run in a programmable way.

Smart contracts are a decentralized solution, meaning they do not require any centralized control or trust authority to manage or verify transactions. Instead, smart contracts use nodes on the blockchain network to verify and execute transactions. Since smart contracts are based on blockchain technology, they usually have the following characteristics:

• Security: Smart contracts use cryptography to protect transactions and data, making them safe and secure.
• Decentralization: Smart contracts do not require any centralized institution to verify and execute transactions, thus reducing trust costs and intermediary fees.
• Transparency: The transaction records of smart contracts are public and can be viewed and audited by anyone.
• Automation: Smart contracts can automate specific tasks, increasing efficiency and reducing human error.

How do smart contracts call other smart contracts?

In a blockchain network, each smart contract has a unique address, similar to an IP address on the Internet. To call another smart contract in a smart contract, you first need to know the address of the target smart contract. This can be achieved by storing addresses in smart contracts or passing addresses between smart contracts.

For example, suppose we have two smart contracts A and B. To call B from A, we need to know the address of B. This can be achieved by storing the address of B in A:

contract A {
  address public bAddress;

  function setBAddress(address _address) public {
    bAddress = _address;
  }

  function callB() public {
    B b = B(bAddress);
    b.doSomething();
  }
}

In the above code, A smart contract contains a public variable bAddress, which is used to store the address of B smart contract. The setBAddress() function is used to set the address of B, and the callB() function is used to call the doSomething() function in the B smart contract. In the callB() function, we use the B b = B(bAddress) statement to convert the address of the B smart contract into an instance of the B type, and then use the b.doSomething() statement to call the doSomething() function in the B smart contract .

In addition to storing addresses in smart contracts, it is also possible to pass addresses between smart contracts. For example, suppose we have two smart contracts A and B, and A wants to call a function in B, and pass A's address as a parameter to B. The code looks like this:

contract A {
  function callB(address _bAddress) public {
    B b = B(_bAddress);
    b.doSomething(msg.sender);
  }
}

contract B {
  function doSomething(address _aAddress) public {
    // do something with _aAddress
  }
}

In the above code, the callB() function in the A smart contract accepts an address as a parameter, and uses the B b = B(_bAddress) statement to convert the address into an instance of type B. It then calls the doSomething() function in the B smart contract, passing it A's address as a parameter.

Application scenarios where smart contracts call other smart contracts

There are a wide range of application scenarios for smart contracts to call other smart contracts. Here are some examples:

• The function of merging multiple smart contracts: When a smart contract needs to perform multiple tasks, it can call other smart contracts to complete these tasks. For example, a smart contract may need to verify the ownership of a digital asset, check whether the digital asset is locked, and transfer the ownership of the digital asset. These tasks can be done by different smart contracts, and then a main smart contract calls these smart contracts and executes these tasks.
• Split smart contracts into smaller components: When a smart contract becomes very large, it can become difficult to maintain and upgrade. To solve this problem, smart contracts can be split into smaller components and have them call each other to complete tasks. This makes the code more manageable and different components can be assigned to different developers for development and testing.
• Execute complex business logic: Some business logic may need to call multiple smart contracts to complete. For example, when a digital asset is transferred, it may be necessary to verify the identity of the sender and receiver, check whether the asset is locked, and record the transaction. These tasks can be done by multiple smart contracts, and a master smart contract calls them and executes these tasks.
• Improve code reusability: When multiple smart contracts need to perform similar tasks, these tasks can be encapsulated in a single smart contract and called by other smart contracts. This increases code reusability and reduces code redundancy.
• Realize cross-chain interaction: When a smart contract needs to interact with smart contracts on other blockchains, it can do so by calling other smart contracts. For example, a smart contract may need to transfer a digital asset from Ethereum to the Bitcoin network. In this case, it can invoke a smart contract that interacts with the Bitcoin network to achieve this functionality.

Precautions for smart contracts calling other smart contracts

• Ensure the correctness of the smart contract address: Before calling other smart contracts, you must ensure that the address of the called smart contract is correct. Otherwise, the smart contract may call the wrong contract, leading to unpredictable results.
• Ensure the security of smart contracts: When calling other smart contracts, it is necessary to ensure that the called smart contracts are safe. Otherwise, smart contracts may be attacked and result in loss of funds or data.
• Handling call exceptions: When a smart contract calls another smart contract, exceptions may occur, such as the called smart contract does not exist or fails to execute. In such cases, these exceptions must be handled and appropriate actions taken, such as logging an error message or rolling back the transaction.
• Ensure that the interaction between smart contracts conforms to business logic: When a smart contract calls other smart contracts, it must ensure that the interaction between them conforms to business logic. Otherwise, it may cause errors in business logic and lead to unpredictable results.

in conclusion

Smart contracts call other smart contracts is an important means to implement complex business logic and improve code reusability. Interaction between smart contracts can be achieved by storing addresses in smart contracts, passing addresses and calling functions in other smart contracts. When using a smart contract to call other smart contracts, it is necessary to ensure the correctness and security of the smart contract address and handle call exceptions. Only in this way can the interaction between smart contracts be guaranteed to comply with business logic and achieve expected functions.