Call


						bytes memory args = abi.encodeWithSignature("set(uint256)", newPrice);
						(bool success, bytes memory retData) = feed.call.value(msg.value)(args);

StaticCall

Same as call, but will revert on state changes 
						
							bytes memory args = abi.encodeWithSignature("set(uint256)", newPrice);
							(bool success, bytes memory retData) = feed.staticcall(args);

DelegateCall

  • same as call, but will run in the context of the calling contract
  • how library is implemented
						
						bytes memory args = abi.encodeWithSignature("set(uint256)", newPrice);
						(bool success, bytes memory retData) = feed.delegatecall(args);
### Context - The environment/data available to the function during execution * account (storage) * stack * memory * message call data
### Account * 2 types of accounts: - externally owned account (EOA) - contract account * Account contains: balance, a nonce, bytecode, and stored data (storage) * EOA has empty bytecode and storage

Account Storage

  • This is where state variables are stored
  • It is persistent between function calls and transactions
  • It is a key-value mapping of 2256 keys; each value is 32 bytes long
### Stack * All computations are performed on the stack * It has a maximum of 1024 elements * Access to stack is limited to the top elements * Access to elements by pop/push to stack
### Memory * Memory is volatile * It is mainly used to store data during execution * Each message call starts with a cleared memory

Message Call Data

  • msg.data: the input data for the function call
  • msg.sender: the sender of the message
  • msg.value: number of wei sent with the message

This

  • this refers to the current contract for non-delegated calls
  • this refers to the caller contract for delegated call

Caller

  • tx.origin is the sender of the transaction (full call chain)
  • msg.sender is the sender of the current message call
### Non-Delegated Message Call ![non-delegatecall](./non-delegatecall.svg "Non Delegate Call")
### Delegated Message Call ![delegatecall](./delegatecall.svg "Delegate Call")
### Sender Context ![sendercontext](./sender-context.svg "Sender Context")

State Variables Storage Layout

  • Solidity generates code that saves variable values in their declaration order.
  • Variable first was declared first, it’s stored in slot 0
  • Items that need less than 32 bytes are packed together. See Rules

						contract Sample {
							uint first;    // storage slot 0
							uint second;   // storage slot 1
						}

Lab

Follow the instructions on the readme file of proxy-delegate