⚽Gas Saving Technique 31: Optimize Storage by Avoiding Booleans

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Introduction: Using booleans for storage in Solidity might seem like an efficient choice given their simple true/false representation. However, due to the underlying mechanics of the Ethereum Virtual Machine (EVM), booleans can lead to increased gas costs when used as storage variables. This tutorial will explore the reasons behind this inefficiency and provide alternative approaches.

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Concept: Booleans in Solidity, when used as storage variables, do not consume a full 256-bit word in the EVM. However, the compiler generates additional operations to ensure data integrity when reading and writing to these slots. This involves an extra SLOAD to read the slot's current value, modifying the relevant bits for the boolean, and then writing the modified value back using SSTORE.

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Underlying Problem:

1. Inherent Compiler Mechanics: Due to potential issues like contract upgrades and pointer aliasing, the Solidity compiler employs certain defenses which lead to these extra operations.

2. Wasted Storage: Booleans don't utilize the full storage slot, leading to inefficiencies.

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Examples & Recommendations:

1. EternalStorage Boolean Mapping:

   • Before:

     solidityCopy codemapping(bytes32 => bool) private _boolStorage;

   • After (Using uint256 as a flag, where 0 can represent false and 1 can represent true):

     solidityCopy codemapping(bytes32 => uint256) private _flagStorage;

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Step-by-Step Guide to Implementing the Storage Optimization Technique:

1. Identify instances where booleans are used as storage variables.

2. Replace boolean storage declarations with uint256.

3. Modify the logic of your contract to treat 0 as false and any non-zero value (typically 1) as true.

4. Update any functions that interact with the changed storage variables to accommodate this new representation.

5. Test your contract thoroughly to ensure that the logic remains consistent and correct.

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Benefits:

1. Gas Savings: Removing the overhead associated with booleans can lead to significant gas savings over the lifespan of a contract.

2. Consistent Storage Usage: By using uint256, the contract optimally uses the available storage slot.

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Conclusion: At first glance, booleans might seem like a gas-efficient choice for storage in Solidity contracts. However, understanding the deeper mechanics of the EVM and the Solidity compiler reveals that other data types, such as uint256, can provide more efficient storage solutions, leading to gas savings.