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/[email protected]
