Title says it; I get an access violation in code marked @safe. Here's a minimal example:

[code]
@safe:

struct Foo(alias Callback)
{
    ~this() {Callback();}
}

unittest
{
    uint stackVar;
    alias FooType = Foo!((){++stackVar;});

    FooType[1] foos;
    foos[0] = FooType.init;
}
[/code]

This results in:
object.Error@(0): Access Violation
----------------
0x00405E2A in pure nothrow @nogc @safe void test.__unittestL9_4().__lambda1() at <path>\test.d(12)
... more stack ...

Line 12 is the alias FooType line, where the delegate is defined.

Where is this coming from? Intuition says it is something to do with calling the delegate after the stack frame has popped and stackVar is unreachable, but I'm not seeing it. Wouldn't foos be destructed before the stack frame is gone?

I don't get the issue if I mark stackVar static, or if I don't perform the assignment to foos[0].

On 1/29/16 11:53 PM, Matt Elkins wrote:
> Title says it; I get an access violation in code marked @safe. Here's a
> minimal example:
>
> [code]
> @safe:
>
> struct Foo(alias Callback)
> {
>      ~this() {Callback();}
> }
>
> unittest
> {
>      uint stackVar;
>      alias FooType = Foo!((){++stackVar;});
>
>      FooType[1] foos;
>      foos[0] = FooType.init;
> }
> [/code]
>
> This results in:
> object.Error@(0): Access Violation
> ----------------
> 0x00405E2A in pure nothrow @nogc @safe void
> test.__unittestL9_4().__lambda1() at <path>\test.d(12)
> .... more stack ...
>
> Line 12 is the alias FooType line, where the delegate is defined.
>
> Where is this coming from? Intuition says it is something to do with
> calling the delegate after the stack frame has popped and stackVar is
> unreachable, but I'm not seeing it. Wouldn't foos be destructed before
> the stack frame is gone?
>
> I don't get the issue if I mark stackVar static, or if I don't perform
> the assignment to foos[0].

This looks like a bug in the compiler. It appears that Foo.init as an rvalue destroying itself results in a call into an invalid stack.

It doesn't require a lambda, or a fixed-size array. And it doesn't require the stack frame holding stackVar to be invalid. This also shows the behavior:

unittest
{
uint stackVar;
void blah() { ++stackVar; }

{
   // introduce inner scope
   FooType foo = FooType.init;
}

}

https://issues.dlang.org/enter_bug.cgi

-Steve

On Saturday, 30 January 2016 at 05:18:08 UTC, Steven Schveighoffer wrote:
> https://issues.dlang.org/enter_bug.cgi
>
> -Steve

Added!
https://issues.dlang.org/show_bug.cgi?id=15627

Thanks for the help.

Alias templates require stack pointer, init probably has it set to null.
Try this:
FooType foo = FooType();

On Saturday, 30 January 2016 at 13:37:43 UTC, Kagamin wrote:
> Alias templates require stack pointer, init probably has it set to null.
> Try this:
> FooType foo = FooType();

Yes, that fixed it. Interesting.