0

我正在构建 Test-First-Teaching performance_monitor 并且可以进行第五次测试，但它失败了。

为什么我的块只运行一次？

这是我的代码：

require "time"
t = Time.now
def measure x=0
start = Time.now
    yield x 
endt = Time.now - start
    end
measure(4){ |x| x.times do Time.now - t end}

这是错误：

*Error____
Performance Monitor
  takes about 0 seconds to run an empty block
  takes exactly 0 seconds to run an empty block (with stubs)
  takes about 1 second to run a block that sleeps for 1 second
  takes exactly 1 second to run a block that sleeps for 1 second (with stubs)
  runs a block N times (FAILED - 1)

Failures:

  1) Performance Monitor runs a block N times
     Failure/Error: n.should == 4
       expected: 4
            got: 1 (using ==)
4

2 回答 2

1

Think about it like this: Your measure method is the one that's in charge of making sure the block that gets passed to it is run the correct number of times. So the block you pass to measure should only include the code that should be run in a single iteration.

For a bare-bones example (theme shamelessly ripped from Gary Bernhardt's "WAT" talk):

def repeat_x_times(x)
    # This runs the passed block x times:
    x.times do
        yield
    end
end

repeat_x_times(16) do
    # This is what should happen in a single iteration:
    puts 0.0 / 0.0
end

puts 'Batman!'

The other cool thing about blocks is that you can always access the variables in the same scope as the block (usually local variables), regardless of where the yield happens:

i = 3
4.times {i += 1} # We can still get to i!
puts i           # Prints "7"

Combining the two concepts for a slightly more involved example:

array = [3, 6, 9, 12, 15]
sum = 0
array.each do |item|
    # In the first iteration, item is 3; in the second it's 6, and so on:
    sum += item
end
puts sum

Now, I know I haven't answered your question directly, but it sounds like you're learning Ruby, so hopefully this is more useful than a cut-n-paste... Anyway, just play around with this until you get it, and pretty soon you'll be wishing all languages had such a useful feature!

于 2013-01-24T14:42:21.357 回答
0

我想出的是： 

    require "time"

    def measure (x=1)
        elapsed = 0
        x.times do
        start = Time.now
        yield
        endt = Time.now
        elapsed += endt - start
   end
   elapsed / x
   if elapsed < 1 
        time = "milliseconds"
   else
        time = "seconds"

    end
    puts "We ran this block #{x} times \nand it took #{elapsed} #{time}"
    end

    measure(50000){puts "Run a block" }
于 2013-01-25T02:42:20.087 回答