Hello,

I get the error "addToBiz(T)(Biz!T biz) is not an lvalue and cannot be modified" when compiling the code below. Can't find a way how to do it right. Am a D newbie and would appreciate some help.

Thank you, Bienlein

class Biz(T) {

    private T value;

    this(T value) {
        this.value = value;	
    }

}

static void addToBiz(T)(Biz!T biz)
{
    // ...
}


int main()
{
    auto biz = new Biz!int(123);
    spawn(&addToBiz, biz);
}

On Wednesday, 8 November 2023 at 16:30:49 UTC, Bienlein wrote:

static void addToBiz(T)(Biz!T biz)
{
    // ...
}


int main()
{
    auto biz = new Biz!int(123);
    spawn(&addToBiz, biz);
}

This is a really bad error message.

The actual problem here is that you can't take the address of a template without instantiating it first. To make your example work, replace &addToBiz with &addToBiz!int, like this:

spawn(&addToBiz!int, biz);

On Wednesday, 8 November 2023 at 16:47:02 UTC, Paul Backus wrote:

spawn(&addToBiz!int, biz);

Thanks, Paul. This helped a step further. When applying your change it looks like this:

Biz!int biz = new Biz!int(123);
spawn(&addToBiz!int, biz);

Then I get this error: 'Error: static assert: "Aliases to mutable thread-local data not allowed."'

For this error I found this in the Internet: https://stackoverflow.com/questions/14395018/aliases-to-mutable-thread-local-data-not-allowed

But this change, did not help:

spawn(&addToBiz!int, cast(shared) biz);

Then I moved "Biz!int biz = new Biz!int(123);" out of the main function. Compiler complains about static this. Okay, then the code outside the main function now looks this way:

class Biz(T) {

private T value;

this(T value) {
    this.value = value;
}

}

static void addToBiz(T)(Biz!T biz)
{
// ...
}

Biz!int biz;

static this() {
biz = new Biz!int(123);
}

int main()
{
// ...
}

However, this results in no gain as the compiler now shows the initial error again: 'Error: static assert: "Aliases to mutable thread-local data not allowed."'

Everything I tried on my own was also to no avail. If someone could gould give me a hint again ... ;-)

Thank you.

On Thursday, 9 November 2023 at 09:40:47 UTC, Bienlein wrote:

spawn(&addToBiz!int, biz);

private T value;

this(T value) {
    this.value = value;
}

If I supply a callback function with the parameter not being an instance from a parameterized class I get the same error. The problem seems to be that the parameter of the callback function takes on object as a parameter and not a built-in type like int or String.

The samples on how to use the spawn function on dlang.org does not contain a sample on how to get things to work with a objecgt being supllied as parameter to the callback function

On Thursday, 9 November 2023 at 10:14:46 UTC, Bienlein wrote:

spawn(&addToBiz!int, biz);

All right. It seems I cannot pass on an object. So I store the object in a global and access it from the callback function passed to spawn.