Passing dynamic arrays

[Steven Schveighoffer]

On Mon, 08 Nov 2010 13:35:38 -0500, Daniel Gibson <metalcaedes at gmail.com>  
wrote:

> bearophile schrieb:
>> Jens Mueller:
>>
>>> I find this behavior rather strange.
>>  I don't know if it's strange, but surely it is a little bug-prone  
>> corner of D. I have had two or three bugs in my code because of that.
>>
>
> If you pass a dynamic array to a function and chance it's size within  
> the function, you have undefined behaviour - you never know if it will  
> affect the original array (from the calling function) or not.

Not exactly.  If you happen to change its size *and* change the original  
data afterwards, then it's somewhat undefined (I'd call it confusing,  
since the behavior is perfectly defined, just hard to describe).

Such cases are very rare.  You are usually changing data on the array in  
place, or appending to the array, but not usually both.

> So IMHO a compiler warning would  be appropriate in that case.
>
> (It would be even better to have more consistent array handling  
> throughout the different kinds of arrays, as I wrote in another branch  
> of this thread, but if that is no option, for example because it  
> contradicts TDPL, a compiler warning is a good compromise)

First, D doesn't have compiler warnings.  Either something is an error, or  
it is not.  You can use the -w switch to turn on extra checks that become  
errors, but that's it.

Second, if you made that a compiler warning, then 90% of D functions would  
exhibit a warning.

This may appear to be a surprising issue, the one time it happens to you,  
but when it does, you learn how arrays work and move on.  In practice,  
it's not a huge killer such as to warrant making it a compiler error or  
warning.

-Steve