d-programming-language.org

[Andrei Alexandrescu]

On 7/4/11 7:38 PM, Mehrdad wrote:
> Since I didn't see this being mentioned anywhere, I thought I'd mention
> it...
>
> On 7/4/2011 1:58 PM, Andrei Alexandrescu wrote:
>> On 7/4/11 2:48 PM, bearophile wrote:
>>> In this case you wrap the code in something that allows it to
>>> overflow without errors, like:
>>>
>>> unsafe(overflows) { // code here }
>>
>> This approach has a number of issues. First, addressing transitivity is
>> difficult. If the code in such a scope calls a function, either every
>> function has two versions, or chooses one way to go about it. Each
>> choice has obvious drawbacks.
>
> C# chooses to limit the scope to the current function, and it works
> pretty well. The use is to modify the behavior of the *operators*, and
> hence, there's no transitivity issue because that's just not what it's
> used for.

Well that's a choice with its inherent tradeoffs.

>> Second, programmers are notoriously bad at choosing which code is
>> affecting bottom line performance, yet this feature explicitly puts the
>> burden on the coder. So code will be littered with amends, yet still be
>> overall slower. This feature has very poor scalability.
>
> Actually, there is **NO** performance issue -- at least not in C#. In
> fact, if you run this program (with or without optimizations), you will
> see that they're literally the same almost all the time:
>
> using System;
>
> static class Program
> {
> static long globalVar = 0; //Make it static so it doesn't get optimized
> static void Main()
> {
> const long COUNT = 100000000;
> for (;;)
> {
> var start = Environment.TickCount;
> for (long i = 0; i < COUNT; i++)
> checked { globalVar = i * i; }
> System.Console.WriteLine("Checked: {0}", Environment.TickCount - start);
>
> start = Environment.TickCount;
> for (long i = 0; i < COUNT; i++)
> unchecked { globalVar = i * i; }
> System.Console.WriteLine("Unchecked: {0}", Environment.TickCount - start);
> }
> }
> }
>
> There is literally no performance issue. Ever.

Isn't it a bit of a stretch to derive a definitive conclusion from one 
small test?


Andrei