zzl0

Latency Comparison Numbers
--------------------------
L1 cache reference                            0.5 ns
Branch mispredict                             5   ns
L2 cache reference                            7   ns             14x L1 cache
Mutex lock/unlock                            25   ns
Main memory reference                       100   ns             20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy              3,000   ns
Send 1K bytes over 1 Gbps network        10,000   ns    0.01 ms
Read 4K randomly from SSD*              150,000   ns    0.15 ms

zzl0

class memoized(object):
    '''Decorator. Caches a function's return value each time it is called.
    If called later with the same arguments, the cached value is returned
    (not reevaluated).
    '''
    def __init__(self, func):
        self.func = func
        self.cache = {}

    def __call__(self, *args):

zzl0

1. 编写一个BankAccount类，加入deposit和withdraw方法，和一个只读的balance属性。

class BankAccount(val balance: Double) {
  def deposit(amount: Double): BankAccount = {
    require(amount > 0)
    new BankAccount(balance + amount)
  }

  def withdraw(amount: Double): BankAccount = {
    require(amount > 0 && amount <= balance)