Solidity Minimalist Tutorial: 4. Function output (return/returns)

Recently, I have been relearning Solidity, consolidating the finer details, and also writing a "Solidity Minimalist Tutorial" for newbies to learn. Lectures are updated 1~3 times weekly.

Everyone is welcomed to follow my Twitter: @0xAA_Science

WTF Academy Discord: Link

All codebase and tutorial notes are open source and available on GitHub (At 1024 repo stars, course certification is unlocked. At 2048 repo stars, community NFT is unlocked.): github.com/AmazingAng/WTFSolidity

---

In this section, we will introduce Solidity function output, including returning multiple values, named returns, and reading full and part of return values using destructuring assignments.

Return values(return and returns)

There are two keywords about function output: return and returns, which differ from:

• returns is added after the function name to declare variable type and variable name;
• return is used for the function body and returns specified variables.

    // returning multiple variables
    function returnMultiple() public pure returns(uint256, bool, uint256[3] memory){
            return(1, true, [uint256(1),2,5]);
        }

In the above code, we stated that the returnMultiple() function will have multiple outputs: returns (uint256, bool, uint256[3] memory) , and then we determined return values in the function body with return (1, true, [uint256 (1), 2,5]) .

Named returns

We can indicate the name of the return variables in returns, so that the solidity automatically initializes these variables, and automatically returns the values of these functions, without adding a return.

    // named returns
    function returnNamed() public pure returns(uint256 _number, bool _bool, uint256[3] memory _array){
        _number = 2;
        _bool = false; 
        _array = [uint256(3),2,1];
    }

In the above code, we declare the return variable type and variable name with the returns (uint256 _number, bool _bool, uint256[3] memory _array) . This way, we will only need to assign values to the variable _ number in the body, _bool and _array and they will automatically return.

Of course, you can also return variables with return in named returns:

    // Named return, still support return
    function returnNamed2() public pure returns(uint256 _number, bool _bool, uint256[3] memory _array){
        return(1, true, [uint256(1),2,5]);
    }

Destructuring assignments

solidity uses rules for destructuring assignments and supports the full or part of return values of the function.

• Read all return values: declare the variables to be assigned and separate them by , in order.

        uint256 _number;
        bool _bool;
        uint256[3] memory _array;
        (_number, _bool, _array) = returnNamed();

• Read part of return values: declare the variables to read in return values and the variables not to read can be left out. In the following code, we only read the return value _bool, but not _ number and _array:

        (, _bool2, ) = returnNamed();

Verify on Remix

• View the results of the three return methods after deploying the contract

Tutorial summary

In this section, we introduced function return values return and returns, including returning multiple variables, named returns, and reading full and part of return values using destructuring assignments.