Passing array as const slows down code?

[Steven Schveighoffer]

On Fri, 27 Apr 2012 15:28:48 -0400, Joseph Rushton Wakeling  
<joseph.wakeling at webdrake.net> wrote:

> On 27/04/12 20:39, Steven Schveighoffer wrote:
>> No, just make sure all the parameters and the result are either  
>> immutable or
>> implicitly castable to immutable (hard to explain this better).
>>
>> Hm... gives me a thought that unit tests should have a helper that  
>> allows
>> ensuring this:
>>
>> static assert(isStrongPure!fn);
>>
>> Or maybe __traits(isStrongPure, fn) if it's too difficult to do in a  
>> library.
>
> Not worth adding a strongpure (purest?) attribute to enable coders to  
> explicitly mark their expectations?

In most cases it's not that important.  strong Pure is simply for  
optimization.

Plus, what that would do is guarantee that the function only compiles if  
the parameters and return value are implicitly convertible to immutable.   
There is no other special requirements, and the parameters and return type  
are sitting right there, next to the strongpure function, it's likely not  
necessary to re-state the intent.

Note that, even if a strong pure function becomes a weak-pure one, it's  
still valid (and compiles, and runs).

It can be viewed similarly to inline, where the compiler makes the  
decision.  Sometimes it's nice to force the issue, but for the most part,  
the compiler will know better what should be inlined.

>> array bounds checks and asserts are turned off during -release  
>> compilation :)
>
> Maybe I've misunderstood what that means, but I would still have  
> expected the program to stop running at least.  What was it doing  
> instead ... ? :-)

It didn't crash because the memory it accessed was still part of the  
program's address space.  out of bounds references don't have to  
necessarily point at invalid memory.

-Steve