Passing array as const slows down code?

[H. S. Teoh]

On Fri, Apr 27, 2012 at 08:29:40PM +0200, Joseph Rushton Wakeling wrote:
> On 27/04/12 20:25, H. S. Teoh wrote:
> >On Fri, Apr 27, 2012 at 07:25:30PM +0200, Joseph Rushton Wakeling wrote:
> >>I was more concerned that the compiler wasn't identifying what to me
> >>was a violation of purity.  I'm fairly sure I can also find a way to
> >>make some of those "nothrow" functions throw an error ...
> >
> >It's not a violation of purity, it's just "weak purity". If you try
> >to access a global variable, for example, it will trigger an error.
> 
> Thanks for the extended description of weak purity -- it's been very
> helpful in understanding the concept better.
> 
> Is there a particular way in which I can explicitly mark a function as
> strongly pure?

The "strong/weak" distinction is deduced by the compiler internally.


> >And nothrow functions *are* allowed to throw Error objects. That's
> >also a deliberate decision. :-)
> 
> ... yes, as I just found out when I decided to test it 2 minutes ago
> :-)  OTOH I found that with or without the nothrow option, when the
> -release flag was used in compiling the code, the error was not thrown
> and the program did not exit -- it just sat there seemingly running
> but doing nothing.  This was unexpected ...
> 
> The deliberate error was in this case a range exception when accessing
> an array.

In -release mode, array bounds checking is turned off for speed reasons.
The idea being that before you compile with -release you've already
extensively tested your program and are sure that simple bugs like array
overruns have been weeded out.


T

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