Hi:
   why writeln need GC?

On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
> Hi:
>    why writeln need GC?

I cannot answer why it needs GC but something can be implemented like:

import core.stdc.stdio;

struct Point {
    int x;
    int y;
}

class Person {
    string name;
    uint age;
}

template GenStructMemberPrint(string structInstanceName, string memberName){
    const char[] GenStructMemberPrint = "printf(\"%d\", " ~structInstanceName ~ "." ~ memberName ~ ");"; // static ifs can be used to use proper formats depending on the typeof struct member
}

// entire thing can be implemented using sprintf to obtain a nice formatted line
void writeln2(A...)(A arguments) @nogc nothrow {
    foreach (a; arguments) {
        static if (is(typeof(a) == class) || is(typeof(a) == interface)) {
            printf("%s \n", typeof(a).stringof.ptr);
        } else
            static if (is(typeof(a) == string)) {
            printf("%s \n", a.ptr);
        } else
        static if (is(typeof(a) == struct)){
            foreach (member; __traits(allMembers, typeof(a))) {
                //writeln(member);
                mixin(GenStructMemberPrint!(a.stringof, member)); // this needs some improvements to imitate writeln
            }
        }
        else {
            static assert( "non-supported type!");
        }
    }

}

void main()
{
    auto pt = Point(10, 20);
    auto per = new Person(); // nogc custom allocator can be used here
	
    writeln2("ssss", per, pt);
}

On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
> Hi:
>    why writeln need GC?

It almost never does, it just keeps the option open in case

* it needs to throw an exception (like if stdout is closed)

* you pass it a custom type with toString that uses GC

@nogc is just super strict and doesn't even allow for rare cases.

On Thursday, 31 October 2019 at 13:46:07 UTC, Adam D. Ruppe wrote:
> On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
>> Hi:
>>    why writeln need GC?
>
> It almost never does, it just keeps the option open in case
>
> * it needs to throw an exception (like if stdout is closed)
>
> * you pass it a custom type with toString that uses GC
>
> @nogc is just super strict and doesn't even allow for rare cases.

It would be nice if one reimplement writeln of Phobos by bypassing gc and use a custom nogc exception as described here*? Of course I can imagine that it would be a breaking change in the language and requires so much work for it to be compatible with other std modules/language features.

*: https://www.auburnsounds.com/blog/2016-11-10_Running-D-without-its-runtime.html

On Thursday, 31 October 2019 at 15:11:42 UTC, Ferhat Kurtulmuş wrote:

> It would be nice if one reimplement writeln of Phobos by bypassing gc and use a custom nogc exception as described here*? Of course I can imagine that it would be a breaking change in the language and requires so much work for it to be compatible with other std modules/language features.
>
> *: https://www.auburnsounds.com/blog/2016-11-10_Running-D-without-its-runtime.html

I can't imagine any possibility we'll ever see a breaking change to writeln. It would have to be an addition to Phobos.

On Thursday, October 31, 2019 9:11:42 AM MDT Ferhat Kurtulmuş via Digitalmars-d-learn wrote:
> On Thursday, 31 October 2019 at 13:46:07 UTC, Adam D. Ruppe wrote:
> > On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
> >> Hi:
> >>    why writeln need GC?
> >
> > It almost never does, it just keeps the option open in case
> >
> > * it needs to throw an exception (like if stdout is closed)
> >
> > * you pass it a custom type with toString that uses GC
> >
> > @nogc is just super strict and doesn't even allow for rare cases.
>
> It would be nice if one reimplement writeln of Phobos by bypassing gc and use a custom nogc exception as described here*? Of course I can imagine that it would be a breaking change in the language and requires so much work for it to be compatible with other std modules/language features.
>
> *: https://www.auburnsounds.com/blog/2016-11-10_Running-D-without-its-runtime .html

You can always just use printf.

- Jonathan M Davis

On Thursday, 31 October 2019 at 16:03:22 UTC, bachmeier wrote:
> On Thursday, 31 October 2019 at 15:11:42 UTC, Ferhat Kurtulmuş wrote:
>
>> It would be nice if one reimplement writeln of Phobos by bypassing gc and use a custom nogc exception as described here*? Of course I can imagine that it would be a breaking change in the language and requires so much work for it to be compatible with other std modules/language features.
>>
>> *: https://www.auburnsounds.com/blog/2016-11-10_Running-D-without-its-runtime.html
>
> I can't imagine any possibility we'll ever see a breaking change to writeln. It would have to be an addition to Phobos.

Yep or Phobos 2 which is more realistic at this point.

On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
> Hi:
>    why writeln need GC?

See also Mir's @nogc formatting module

https://github.com/libmir/mir-runtime/blob/master/source/mir/format.d

On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
> Hi:
>    why writeln need GC?

Upon this post, I thought writing a gc-free writeln would be a good learning practice. Although it is not a feature-complete one, it was a lot of fun to do it :)

https://github.com/aferust/stringnogc

On Sunday, 3 November 2019 at 05:46:53 UTC, 9il wrote:
> On Thursday, 31 October 2019 at 03:56:56 UTC, lili wrote:
>> Hi:
>>    why writeln need GC?
>
> See also Mir's @nogc formatting module
>
> https://github.com/libmir/mir-runtime/blob/master/source/mir/format.d

hi, is mir right now fully implemented using betterC?

thanks!
--
binghoo