Minimize Gas in Your Smart Contracts

Simple Hacks to reduce the Gas you pay for Smart Contracts

I went from paying excessive amounts in gas to paying a reasonable amount after doing a course on solidity development.

I’ll tell you the main tricks here so you don’t waste your time doing the entire course.

1. Smaller uints

If you’ve got multiple uints inside a struct use a small-sized uint. This allows Solidity to use less storage.

Convert this:

struct NormalStruct {
 uint a;
 uint b;
 uint c;
}

To this:

struct MiniMe {
 uint32 a;
 uint32 b;
 uint c;
}

MiniMe will cost less gas than NormalStruct because of struct packing

2. View Functions Don’t Cost You a Thing

View functions don’t cost any gas when they’re called externally by a user.

This is because view functions don’t actually change anything on the blockchain — they only read the data.

Wherever possible use a view function. Here’s an example:

# [https://github.com/spiyer99/CryptoZombies/blob/master/contracts/zombie\_helper.sol#L36](https://github.com/spiyer99/CryptoZombies/blob/master/contracts/zombie_helper.sol#L36)

function getZombiesByOwner(address _owner) external view returns(uint[] memory) {
  uint[] memory result = new uint[](ownerZombieCount[_owner]);
  uint counter = 0;
  for (uint i = 0; i < zombies.length; i++) {
    if (zombieToOwner[i] == _owner) {
      result[counter] = i;
      counter++;
    }
  }
  return result;
}

This function allows us to find all the zombies that someone owns.

We do this by iterating through every single zombie.

Yes this is naive. We could simply create a hash map. That would reduce the lookup to O(1).

But it’s also cheaper than a hash map. So it’s better. The end.

Conclusion

And that’s it! These two things saved me a considerable amount of gas. I hope they help you too.