Better way of passing multiple labels to a function (no string parsing) about contracts

[nostdm]

@mischat

[nostdm]

Here's an example implementation of using an array of bytes [[0x54, 0x4B, 0x4E], [0x42, 0x4E, 0x54], [0x5A, 0x52, 0x58]] instead of parsing a string TKN.BNT.ZRX.

I also tested the gas cost of each approach:

String parsing cost (adding 3 tokens):
Total: 618 000 gas
Execution: 427 000 gas

Byte array cost (adding 3 tokens):
Total : 560 000 gas
Execution: 385 000 gas

Byte array example:

pragma solidity ^0.4.24;

contract Labels {
    
    struct Token {
        string label;
        uint8 decimals;
    }
    
    mapping (address => Token) public labels;
    
    function setLabels(address[] _tokens, bytes32[] _labels, uint8[] _decimals) public {
        for (uint i = 0; i < _labels.length; i++) {
            labels[_tokens[i]].label = bytes32ToString(_labels[i]);
            labels[_tokens[i]].decimals = _decimals[i];
        }
    }
    
    function bytes32ToString(bytes32 _bytes) public pure returns (string) {
        bytes memory bytesString = new bytes(32);
        uint charCount = 0;
        for (uint i = 0; i < 32; i++) {
            byte char = byte(bytes32(uint(_bytes) * 2 ** (8 * i)));
            if (char != 0) {
                bytesString[charCount] = char;
                charCount++;
            }
        }
        bytes memory bytesStringTrimmed = new bytes(charCount);
        for (i = 0; i < charCount; i++) {
            bytesStringTrimmed[i] = bytesString[i];
        }
        return string(bytesStringTrimmed);
    }
}

[mischat]

Where did you get this from, I am not sure that I am on the same page as you here. I think I prefer the current implementation. Would be easier for the person interacting with the contract from a programming language ...

[nostdm]

I wrote it as an example. Well it's cheaper in terms of gas and I would argue also more intuitive because other parameters are also arrays.

Also when interacting from a programming langue it's as easy as []byte("MyLabel") to covert string to byte array