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Allow using Unique with interfaces #4764

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Merged
wilzbach merged 5 commits into from
Jul 21, 2017
Merged

Allow using Unique with interfaces #4764

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9ea653e
Allow using Unique with interfaces
tmccombs Sep 5, 2016
b6c2e38
Add a little documentation
tmccombs Sep 6, 2016
894bdfe
Merge branch 'master' into unique-interface
tmccombs Mar 16, 2017
7cbea74
Remove trailing space
tmccombs Mar 17, 2017
70a9e2a
Improve unit test for Unique with interface
tmccombs Mar 17, 2017
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52 changes: 49 additions & 3 deletions std/typecons.d
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Original file line number Diff line number Diff line change
Expand Up @@ -61,16 +61,17 @@ $(D T) to deallocate or clean up any non-GC resources.
If it is desirable to persist a $(D Unique!T) outside of its original
scope, then it can be transferred. The transfer can be explicit, by
calling $(D release), or implicit, when returning Unique from a
function. The resource $(D T) can be a polymorphic class object, in
which case Unique behaves polymorphically too.
function. The resource $(D T) can be a polymorphic class object or
instance of an interface, in which case Unique behaves polymorphically
too.

If $(D T) is a value type, then $(D Unique!T) will be implemented
as a reference to a $(D T).
*/
struct Unique(T)
{
/** Represents a reference to $(D T). Resolves to $(D T*) if $(D T) is a value type. */
static if (is(T:Object))
static if (is(T == class) || is(T == interface))
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@PetarKirov PetarKirov Mar 16, 2017

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Does this work with extern(C++) or extern(Windows) classes & interfaces? If not we should not allow them.

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@tmccombs tmccombs Mar 16, 2017

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I'm not sure.

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@JackStouffer JackStouffer Mar 16, 2017

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@ZombineDev Good luck detecting them. This is something that @bbasile has been working on.

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@jmdavis jmdavis Mar 16, 2017

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I don't know about extern(Windows) - isn't that similar to extern(C) which wouldn't work with classes (I really haven't done much with Windows and D, and Windows linking is way more complicated in general than *nix)? However, as for something like extern(C++) or COM interfaces, wouldn't checking

is(T : Object) && (is(T == class) || is(T == interface))

do the trick?

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@jmdavis jmdavis Mar 16, 2017

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That is, if the idea is to exclude them anyway.

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@tmccombs tmccombs Mar 17, 2017

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@jmdavis the problem is that Object is a class, so if T is an interface it won't extend Object.

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@tmccombs tmccombs Mar 17, 2017 •
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I don't know a lot about extern(c++) or extern(Windows), but from reading http://dlang.org/spec/interfaceToC.html, it seems like extern(Windows) isn't really relevant since it is more about function calling conventions, and from http://dlang.org/spec/cpp_interface.html it seems like this might work with C++ classes. Although it isn't really clear if it is safe to call destroy on a C++ class. Of course, Unique certainly won't clean up the memory for a C++ class, but that is true regardless of if RefT is T or T*

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@MetaLang MetaLang Jul 21, 2017

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IMO this shouldn't be stalled on whether it works with extern(C++)/extern(Windows) classes & interfaces. If they didn't work before then this PR doesn't change the status quo.

alias RefT = T;
else
alias RefT = T*;
Expand Down Expand Up @@ -280,6 +281,51 @@ private:
assert(!ub2.isEmpty);
}

@system unittest
{
debug(Unique) writeln("Unique interface");
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@wilzbach wilzbach Jul 21, 2017

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FWIW: @JackStouffer has been working on getting rid of these superfluous debug statements

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@MetaLang MetaLang Jul 21, 2017

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Good. I was going to request that they be removed but it's easy to submit a PR removing them all at once so I didn't bother.

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@wilzbach wilzbach Jul 21, 2017

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Yep, it seems it was common style in this module

interface Bar
{
int val() const;
}
class BarImpl : Bar
{
static int count;
this()
{
count++;
}
~this()
{
count--;
}
int val() const { return 4; };
}
alias UBar = Unique!Bar;
UBar g(UBar u)
{
debug(Unique) writeln("inside g");
return u.release;
}
void consume(UBar u)
{
assert(u.val() == 4);
// Resource automatically deleted here
}
auto ub = UBar(new BarImpl);
assert(BarImpl.count == 1);
assert(!ub.isEmpty);
assert(ub.val == 4);
static assert(!__traits(compiles, {auto ub3 = g(ub);}));
debug(Unique) writeln("Calling g");
auto ub2 = g(ub.release);
debug(Unique) writeln("Returned from g");
assert(ub.isEmpty);
assert(!ub2.isEmpty);
consume(ub2.release);
assert(BarImpl.count == 0);
}

@system unittest
{
debug(Unique) writeln("Unique struct");
Expand Down