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master_solidity/saving_gas.md
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@ -12,14 +12,19 @@
## Function names ### Function names
- brute force hashes of function names to find those that starts `0000`, so this can save around 50 gas - brute force hashes of function names to find those that starts `0000`, so this can save around 50 gas
----
### Other contracts
- avoid calls to other contracts - avoid calls to other contracts
--- ---
## Pack variables ### Pack variables
The below code is an example of poor code and will consume 3 storage slot: The below code is an example of poor code and will consume 3 storage slot:
@ -59,14 +64,14 @@ Constant values can sometimes be cheaper than immutable values:
--- ---
## **Use bytes32 rather than string/bytes** ### **Use bytes32 rather than string/bytes**
- If you can fit your data in 32 bytes, then you should use bytes32 datatype rather than bytes or strings as it is much cheaper in solidity. - If you can fit your data in 32 bytes, then you should use bytes32 datatype rather than bytes or strings as it is much cheaper in solidity.
- Any fixed size variable in solidity is cheaper than variable size. - Any fixed size variable in solidity is cheaper than variable size.
--- ---
## Use external function modifier ### Use external function modifier
- For all the public functions, the input parameters are copied to memory automatically, and it costs gas. - For all the public functions, the input parameters are copied to memory automatically, and it costs gas.
- If your function is only called externally, then you should explicitly mark it as external. - If your function is only called externally, then you should explicitly mark it as external.
@ -75,13 +80,13 @@ Constant values can sometimes be cheaper than immutable values:
--- ---
## Delete variables that you don’t need ### Delete variables that you don’t need
- If you don’t need a variable anymore, you should delete it using the delete keyword provided by solidity or by setting it to its default value. - If you don’t need a variable anymore, you should delete it using the delete keyword provided by solidity or by setting it to its default value.
--- ---
## **No need to initialize variables with default values** ### **No need to initialize variables with default values**
- If a variable is not set/initialized, it is assumed to have the default value (0, false, 0x0 etc depending on the data type). If you explicitly initialize it with its default value, you are just wasting gas. - If a variable is not set/initialized, it is assumed to have the default value (0, false, 0x0 etc depending on the data type). If you explicitly initialize it with its default value, you are just wasting gas.
@ -92,8 +97,20 @@ uint256 world; //good, cheap
--- ---
## **Make use of single line swaps** ### Make use of single line swaps
- This is space-efficient:
``` ```
(hello, world) = (world, hello) (hello, world) = (world, hello)
``` ```
<br>
---
## Tools
<br>
* [truffle contract size](https://github.com/IoBuilders/truffle-contract-size)