An Issue I Wish To Raise Awareness On

[Jack Stouffer via Digitalmars-d]

TL;DR: Issue 17658 [1] makes using shared very 
annoying/practically impossible.

Over the weekend, I attempted to fix Issue 15768 [2], which is an 
underlying problem in the std.stdio.File struct that stops it 
from closing properly when shared across threads. This is a big 
problem for users because stdin/out/err are all __gshared File, 
and are therefore unsafe. This makes for a really annoying 
situation where writeln("a") is @safe but stderr.writeln("a") 
isn't.

The obvious solution is to make stdin/out/err shared(File) and 
modify File to have shared overloads which either lock or use 
atomic ops safely. When I tried to write said functions, I ran 
into compilation issues that I couldn't diagnose until I ran 
across this thread by Atila [3]. The problem is, unlike a 
constructor, destructors and post-blits can't be overloaded with 
shared variants. Consider:

```
struct A
{
     this(string a) {}
     this(string a) shared {}

     ~this() {}
     ~this() shared {}

     this(this) {}
     this(this) shared {}
}

void main()
{
     shared f = A("");
}
```

Error: destructor f152.A.~this conflicts with destructor 
f152.A.~this at /d422/f152.d(6)
Error: function f152.A.__postblit conflicts with function 
f152.A.__postblit at /d422/f152.d(9)

This is further compounded with this

```
struct A
{
	~this() {}
}

void main()
{
	auto a = A();
	shared b = A();
}
```

Error: non-shared method f585.A.~this is not callable using a 
shared object

The only way to work around this is to create a new type that is 
defined as shared struct and copy over all of the code from the 
original type. This really hobbles shared in any real world 
context.

I ask that someone who knows the DMD code base could please take 
a look at this and see if this is something that can be fixed 
easily and without breakage.

[1] https://issues.dlang.org/show_bug.cgi?id=17658
[2] https://issues.dlang.org/show_bug.cgi?id=15768
[3] 
https://forum.dlang.org/post/sqazguejrcdtjimtjxtz@forum.dlang.org