Solidity – Does Executing View or Pure Functions Cost Gas?

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Let's suppose i have the following code in ethereum's solidity function:

function getArray() external pure returns(uint[]) {
  // Instantiate a new array in memory with a length of 3
  uint[] memory values = new uint[](3);
  // Add some values to it
  values.push(1);
  values.push(2);
  values.push(3);
  // Return the array
  return values;
}

As it's pure, it doesn't even read data from storage, doesn't change anything in storage. So imagine I deployed this contract. then there're people who want to invoke this function from web3.js or remix for example. Will this function cost them gas? I've read that view functions and pure functions are the way that don't change the storage. so they're free (no gas). If users use above function, why is it free? i still make the calculation and save temprorary data to memory.

Best Answer

It depends,

If they call a pure function itself, like the one in your example, getArray(), then no, it won't cost anything.

However, if they call a function which isn't pure or view, and that function internally calls the getArray() function, then they will have to pay for the whole transaction.

Related Solutions

Solidity – Handling Unimplemented Functions in Contracts

The problem is that totalSupply() implementation is missing. Seems like autogenerated getters do not count. So you need to explicitly create the function.

contract StandardToken is Token {
    uint256 _totalSupply;

    function totalSupply() constant returns (uint256 totalSupply) {
        totalSupply = _totalSupply;
    }
}

Passing Storage Structure Addresses Between Solidity Contracts

Instinctively, I believe that the only solution is to pass the structure to the function "by address"

You cannot access the physical addresses of storage variables (like you can with C), this is not allowed in Solidity. The address type is only used to refer to the addresses of other accounts (contract or external), and is not used to refer to memory addresses.

A work around would be to use a smart contract to store your data instead of a struct. This way you would be able to pass the address of the smart contract around instead of having to pass the data around. I've posted an example below:

contract Person {
    uint public age;
    uint public weight;

    function Person(uint _age, uint _weight) public {
        age = _age;
        weight = _weight;
    }
}

contract PersonHolder {

    address[] public people; // Could use Person[] here

    function addPerson(uint age, uint weight) public {
        people.push(new Person(age, weight));
    }

    function getPerson(uint index) public view returns (Person) {
        require(people.length > index);

        return Person(people[index]);
    }
}

Best Answer

Related Solutions

Solidity – Handling Unimplemented Functions in Contracts

Passing Storage Structure Addresses Between Solidity Contracts

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