Function Mutability.md

24 - Function Mutability

Function Mutability Specifiers: Functions can be specified as being pure or view:

1. view functions can read contract state but cannot modify it. This is enforced at runtime via STATICCALL opcode. The following are considered state modifying:

   1. Writing to state variables
   2. Emitting events
   3. Creating other contracts
   4. Using selfdestruct
   5. Sending Ether via calls
   6. Calling any function not marked view or pure
   7. Using low-level calls
   8. Using inline assembly that contains certain opcodes.

2. pure functions can neither read contract state nor modify it. The following are considered reading from state:

   1. Reading from state variables
   2. Accessing address(this).balance or <address>.balance
   3. Accessing any of the members of block, tx, msg (with the exception of msg.sig and msg.data)
   4. Calling any function not marked pure
   5. Using inline assembly that contains certain opcodes.

3. It is not possible to prevent functions from reading the state at the level of the EVM. It is only possible to prevent them from writing to the state via STATICCALL. Therefore, only view can be enforced at the EVM level, but not pure.

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Slide Screenshot

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Slide Deck

• View or Pure
• View: Read State
  • Not Modify -> STATICCALL
• Pure: Not Modify
  • Not Read -> !EVM
• Mutability: Write/Read
  • Security Implications

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References

• Youtube Reference

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Tags

System Operations Solidity By Example - View and Pure Functions

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Solidity by Example

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.3;  
contract ViewAndPure {
	uint public x = 1;  
	
	// Promise not to modify the state.
	function addToX(uint y) public view returns (uint) {
		return x + y;
	}
	
	// Promise not to modify or read from the state.
	function add(uint i, uint j) public pure returns (uint) {
		return i + j;
	}
}