On 10/10/2014 06:30 AM, Steven Schveighoffer wrote:
> On 10/10/14 1:00 AM, Ali Çehreli wrote:
>> On 10/09/2014 08:06 PM, Joel wrote:
>>> On Tuesday, 30 September 2014 at 17:27:09 UTC, Adam D. Ruppe wrote:
>>>> On Tuesday, 30 September 2014 at 17:22:44 UTC, Gary Willoughby wrote:
>>>>> What is a sink delegate?
>>>>
>>>> Instead of
>>>>
>>>> string toString() { return "foo"; }
>>>>
>>>> for example, you would use:
>>>>
>>>> void toString(void delegate(string) sink) { sink("foo"); }
>>>>
>>>> The sink argument there is then free to view and discard the data or
>>>> to make a private copy using whatever scheme it desires.
>>>
>>>
>>> How do you use that toString? Maybe an example? Below is my failed
>>> effort.
>>>
>>> import std.stdio;
>>>
>>> struct Try {
>>> string name;
>>> long age;
>>>
>>> void toString(void delegate(string) sink) {
>>> sink("foo");
>>> }
>>> }
>>>
>>> void main() {
>>> Try t = Try("Joel", 35);
>>> writeln(t);
>>> }
>>
>> The signature of that toString is different from what I have been seeing
>> and using. The following works:
>>
>> void toString(void delegate(const(char)[]) sink) const {
>
> The delegate parameter is what is important. The function that is going
> to be passed in takes a const(char)[],
That is what I meant.
> which actually should, but does
> not, implicitly cast to a delegate(string) (see issue
> https://issues.dlang.org/show_bug.cgi?id=3075).
>
> The const outside is irrelevant to whether it will accept it or not,
> that is a contract between the toString function and your object. If you
> want a non-const toString, I think that should work.
>
> (actually, testing it...) Yep, it works without the const on the outside.
But not for const objects. The following program does not call the user
defined toString:
import std.stdio;
import std.conv;
struct S
{
int i;
void toString(void delegate(const(char)[]) sink)
{
sink(i.to!string);
}
}
void main()
{
const c = S(42);
writeln(c);
}
Add a const at the end, now it calls the user defined one.
>
> -Steve
Ali
