On 05/05/2013 12:30 AM, Walter Bright wrote:
> On 5/4/2013 3:03 PM, deadalnix wrote:
>>> Where you miss the point, is that these annotations may be omitted
>>> (and they
>>> are most of the time). When nothing is specified, the lifetime of the
>>> returned
>>> reference is considered to be the union of the lifetime of parameters
>>> lifetime, which is what you want in 99% of cases.
>>
>> Note : We may also choose the lack of explicit lifetime means runtime
>> check as
>> proposed, instead of being an error.
>
> D omits the check when it can prove that the returned ref is not a ref
> to one of the parameters that is local.
ref int foo(ref int a, ref int b);
It's a very nice observation that calling foo with only non-local
references means that the returned reference is non-local too.
In a way this works like inout but with a safe default so
that no annotation is needed.
In fact it's also possible to know that these don't return a reference
to their parameter.
ref double foo(ref int a);
Struct S {}
ref double foo(ref S a);
It can become somewhat complicated to check though.
Anyhow I think using flow-analysis to omit runtime checks is a nice
approach.
