On 01/20/2011 11:31 AM, bearophile wrote:
> Andrej Mitrovic:
>
>> I think what might help out in D is if we had a way to mark some
>> functions so the compiler guarantees that their return values *are
>> not* to be discarded. For example, this code will compile:
>>
>> import std.stdio;
>> import std.string;
>> void main()
>> {
>> string s = "Mary has a lil lamb.";
>> replace(s, "lil", "li'l"); // returns a copy, but discards it
>> }
>>
>> If the replace function is marked with some kind of @nodiscard
>> annotation, then his would be a compile error since it doesn't make
>> sense to construct a new string, return it, and discard it.
>>
>> But maybe that's going overboard. How often do these kinds of bugs
creep in?
>
> Such bugs are common enough. GNU C has the warn_unused_result
attribute (that is like your @nodiscard if you use -Werror to turn
warnings into errors):
> http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
>
> Some C lints require a void cast where you don't want to use a
function result:
> cast(void)replace(s, "lil", "li'l");
>
> In a language the default is different and where you don't want to
use a function result you have to add an annotation:
> unused replace(s, "lil", "li'l");
>
> Something like @nodiscard is more useful in C than D because in C
there are no true built-in exceptions, so error return values are
common, and ignoring them is a mistake. In some cases like replace() or
the C realloc() ignoring a result is always a programmer error. So
something like @nodiscard is useful in D too.
But I thought D had such a feature already. Probably I'm confusing, but
I think I've had compiler warning in such cases, procisely (ingoring a
func result).
denis
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