What does returns (uint256) in Solidity means?

Have you ever seen something like this?

function getBorrowingCapacity(address user) external view returns (uint256) {
    // Example calculation: Borrowing capacity is 75% of collateral
    return (collateral[user] * borrowFactor) / 100;
}

in this function we have external view returns(uint256)
What is (unit256) doing?

When working with Solidity, the Ethereum blockchain's most widely used smart contract programming language, you’ll often encounter function declarations that specify a returns keyword followed by a data type, such as uint256. If you’ve ever wondered why this is necessary or how it works, this guide will break it all down for you.

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What Does returns (uint256) Mean?

The returns (uint256) in a Solidity function declaration defines the type of value the function will produce and send back to the caller after it is executed. This lets the caller know exactly what type of data to expect in response.

Here’s an example of a function declaration:

function getBorrowingCapacity(address user) external view returns (uint256).

This function, getBorrowingCapacity, is designed to return a single unsigned integer value (a uint256). This return value might represent something like the borrowing capacity of the specified user.

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Why Is uint256 Used?

In Solidity, uint256 is a widely used data type. Here's why it’s appropriate for functions like this:

1. Non-Negative Values: Since uint256 represents unsigned integers, it can only hold non-negative values. This is ideal for cases like borrowing capacity, balances, and other numbers that cannot logically be negative.

2. Large Range: The uint256 type can store extremely large numbers, from 0 to . This ensures that even the largest possible borrowing capacities can be accurately stored and returned.

3. Standard Practice: Solidity defaults to uint256 for most numerical computations because it is safer and more scalable.

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How returns (uint256) Works in Practice

Let’s explore a practical example. Imagine you are building a decentralized lending platform where users can borrow tokens based on the value of their deposited collateral. The getBorrowingCapacity function could calculate the maximum amount a user is allowed to borrow.

Here’s how such a function might be implemented:

// Mapping to store each user's collateral balance in tokens

mapping(address => uint256) public collateral;



// Borrowing factor: users can borrow up to 75% of their collateral value
uint256 public borrowFactor = 75;

function getBorrowingCapacity(address user) external view returns (uint256) {
    // Example calculation: Borrowing capacity is 75% of collateral
    return (collateral[user] * borrowFactor) / 100;
}

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Example Scenario

Let’s say Alice deposits 1000 tokens as collateral, and the borrowFactor is set to 75%. When the function is called with Alice's address, it calculates her borrowing capacity as follows:

1. Collateral: 1000 tokens.

2. Borrowing Factor: 75%.

3. Calculation: .

If you call the function like this:

contractInstance.getBorrowingCapacity(alice);

The function will return:

750

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Why Use returns in Solidity?

In Solidity, the returns keyword is essential for creating readable and reusable functions. Here are the main reasons to use it:

1. Data Communication: Functions often need to communicate results (like computed values) back to the caller. Using returns explicitly defines the type of value the function will provide.

2. Clear Expectations: The return type ensures that developers or external contracts interacting with the function know exactly what type of data they can expect. This reduces ambiguity and makes debugging easier.

3. Chaining and Reuse: Returned values can be stored, reused, or even passed as inputs to other functions. For example:

uint256 capacity = contractInstance.getBorrowingCapacity(alice);
if (capacity > 500) {
// Proceed with borrowing
}

1. Efficiency: Returning data directly from a function eliminates the need for extra state variables, making the function more efficient and less prone to bugs.

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Real-World Use Cases for returns (uint256)

Here are some common scenarios where uint256 is returned in Solidity:

1. Token Balances: A function might return the balance of tokens a user holds:

function balanceOf(address user) external view returns (uint256);

1. Borrowing Capacity: As in our example, it might calculate how much a user can borrow:

function getBorrowingCapacity(address user) external view returns (uint256);

1. Interest Rates: It might compute and return interest rates for loans:

function getInterestRate() external view returns (uint256);

1. Auction Bids: It could return the highest bid in an auction:

function getHighestBid() external view returns (uint256);

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Conclusion

The returns (uint256) in Solidity serves as a powerful tool for defining the outputs of a function. It communicates expectations, ensures clarity, and makes functions reusable and efficient. Whether you’re working with balances, borrowing capacities, or auction bids, understanding how to use return types effectively is key to writing robust smart contracts.