[Issue 20858] New: std.parallelism.task: Can't move value to task param

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20858

          Issue ID: 20858
           Summary: std.parallelism.task: Can't move value to task param
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: blocker
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: nin-jin at ya.ru

src\phobos\std\parallelism.d(444,29): Error: struct jin.go.Output!long.Output
is not copyable because it is annotated with @disable

src\phobos\std\parallelism.d(832,16): Error: template instance
std.parallelism.Task!(wrapper, void function(Output!long) @system, Output!long)
error instantiating

Problem in this phobos code:

    private static void impl(void* myTask)
    {
        import std.algorithm.internal : addressOf;

        Task* myCastedTask = cast(typeof(this)*) myTask;
        static if (is(ReturnType == void))
        {
            fun(myCastedTask._args); // !!!
        }
        else static if (is(typeof(&(fun(myCastedTask._args)))))
        {
            myCastedTask.returnVal = addressOf(fun(myCastedTask._args));
        }
        else
        {
            myCastedTask.returnVal = fun(myCastedTask._args);
        }
    }

See workaround in VibeD to call function with move semantic:
https://github.com/vibe-d/vibe-core/blob/master/source/vibe/core/taskpool.d#L210

mixin(callWithMove!ARGS("c", "args.expand")); // !!!

package string callWithMove(ARGS...)(string func, string args)
{
        import std.string;
        string ret = func ~ "(";
        foreach (i, T; ARGS) {
                if (i > 0) ret ~= ", ";
                ret ~= format("%s[%s]", args, i);
                static if (needsMove!T) ret ~= ".move";
        }
        return ret ~ ");";
}

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