Hitchhiker's Guide to the EVM

@alexroan on Twitter

Don't read storage variables too often

• better to create a memory variable and set its value to the storage variable
• update the storage variable at the end, if needed

Pack your structs

• 32 is the magic number
• storage slots are 32 bytes each (SSTORE/SLOAD)
• order of a struct matters:

      // inefficient storage, uses 3 slots
  `address wallet   // SLOT 1 20/32`
  `address backup   // SLOT 2 20/32`
  `uint96 first     // SLOT 2 32/32`
  `uint96 sec       // SLOT 3 12/32`
  
  // efficient storage, uses 2 slots
  `address wallet   // SLOT 1 20/32`
  `uint96 first     // SLOT 1 32/32`
  `address backup   // SLOT 2 20/32`
  `uint96 sec       // SLOT 2 32/32`

Use constant or immutable

• this has huge gas savings benefits
• making constructor initialized variables immutable when there are no plans to update

Don't store unneccesary data

• try to use events instead

Make variables obvious

• an example: Chainlink uses s_ for storage variables