Solidity

Doc: http://solidity.readthedocs.io/en/develop/index.html

Cheatsheet: https://github.com/manojpramesh/solidity-cheatsheet

Data

Storage vs. Memory & Stack

• Storage
  • state variables
  • variable with "storage" modifier
• Memory
  • variable with "memory" modifier
  • function arguments, by default
  • local variables of struct, array or mapping type storage by default
• Stack
  • local variables by value (NEITHER array, nor struct nor mapping)

Data Types

• bool (true false)
• integers
  • int / uint = int256 / uint256
  • intN / uintN : N in steps of 8, bits
• Mapping
  • declaration: mapping(_KeyType => _ValueType)
  • use
    • mapping[key] = value
  • work
    • seen as a hash table
    • virtually initialized such every possible key exists and value all zeros
    • key not stored, only keccak256 hash of key is used to lookup value
    • no key/value "set"
    • possible marked as public

Contract

• has address, has no key
• "this" means current instance of the type derived from the Address (the contract type)
  • explicitly converts to address

Library

• deployed only once at a specific address
  • though same source code can be deployed multiple times at different addresses, for no reason
• no instance, stateless
• code reused
  • using EVM DELEGATECALL (CALLCODE until Homestead)
  • or called directly if do not modify state (i.e. they are "view" or "pure" functions)
    • L.f() - L name of library
    • be seen as implicit base contracts of the contracts that use them
      • internal functions of libraries visible to all contracts
• code executes in the calling contract's context
  • "this" points to calling contract
  • access to calling contract's storage
• when in same source code with some contract & deploy that contract, there will be two deployments - one for library one for contract