👓Gas Saving Technique 29: x = x + y is cheaper than x += y

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Introduction: At first glance, both x = x + y and x += y seem to perform the same arithmetic operation in Solidity. While their end result is indeed the same, the gas cost associated with these two statements can differ. In this tutorial, we delve into the nuances between the two, explaining why favoring the former can lead to enhanced gas efficiency.

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Concept: In Solidity, the compound assignment operation x += y is syntactic sugar for x = x + y. However, the former tends to be slightly more expensive in gas terms. The additional cost stems from the overhead introduced by the compound assignment itself. Therefore, directly using x = x + y can be a more gas-efficient approach.

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Underlying Problem:

1. Compound Assignments: The added overhead of compound assignment operations (+=, -=, etc.) leads to marginally more gas consumption.

2. Accumulation Over Transactions: In contracts with numerous transactions or in widely-used protocols, the extra gas from using compound assignments can accumulate significantly, affecting overall efficiency.

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Example:

Using Compound Assignment:

solidityCopy codeself.balanceOf[_from] -= _amount;
self.balanceOf[_to] += _amount;

Optimized with Direct Assignment:

solidityCopy codeself.balanceOf[_from] = self.balanceOf[_from] - _amount;
self.balanceOf[_to] = self.balanceOf[_to] + _amount;

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Recommendation:

1. Review your contracts to identify occurrences of compound arithmetic assignments, like += or -=.

2. Replace them with their direct assignment equivalents, adjusting any related logic if necessary.

3. Thoroughly test your contracts post-modification to ensure no unintended behaviors have been introduced.

4. Cultivate a practice of using direct arithmetic assignments when drafting new contracts, given that they can offer more predictable gas costs.

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Conclusion: Gas efficiency is paramount in the realm of smart contracts. Embracing simple optimizations—like favoring direct assignments over compound ones—can lead to tangible gas savings, particularly in frequently executed contracts. By paying attention to these subtle differences, developers can produce not only functional but also economically efficient smart contracts, providing the best experience for users and the network.