Implementing VMState and Refactoring Computation

[hwwhww]

What was wrong?

1. This PR is for Implement State object #236 - Implement VMState object.
2. After discussion with @gsalgado and @pipermerriam in State Object #240, I open a new PR includes refactoring Computation class.

How was it fixed?

1. New VMState class - class represents the VM state while the VM is at rest
   1. Move codes of accessing AccountStateDB from BaseVM to VMState class.
      • Snapshot and Revert
      • VMState.get_ancestor_hash()
      • Access to the current block header information (coinbase/timestamp/block_number/difficulty/gas_limit)
2. Computation refactoring - represents the VM state while the VM is running
   1. Make Computation configurable and specified for each VM.
   2. Move all of the state transition codes from VM to Computation. I found that message and vm_state could be just assigned in initialization function:Computation.__init__(vm_state, message, opcodes, precompiles)
      • @classmethod Computation.apply_computation(vm_state, message, opcodes, precompiles): Modify it to be a classmethod. Hope @pipermerriam can take a look if it's a weird anti pattern…?
      • Computation.apply_message()
      • Computation.apply_create_message()
      • Computation.opcodes
      • Computation.precompiles
      • Computation.get_opcode_fn()
   3. Modify apply_child_computation(child_msg).
      • It calls a classmethod Computation.generate_child_computation(vm_state, child_msg, opcodes, precompiles) to generate the child_compuation and then call Computation.add_child_computation(child_computation).
3. Rename StateDB to AccountStateDB.

TODO

• Next PR will refactor block object (Make them dumb data containers). It may include:
  1. Move VM.apply_transaction(transaction) function to VMState.apply_transactionn(transaction)
  2. Move VM.execute_transaction(transaction) function to VMState.execute_transaction(transaction)
  3. Move Block.add_transaction(transaction, computation) to VMState.execute_transaction(transaction, computation)
  4. Move Block.make_receipt(transaction, computation) to VMState.make_receipt(transaction, computation)

Cute Animal Picture

[pipermerriam]

whenever you're ready.

[gsalgado]

Looks great, thanks for considering my suggestions!