I'm writing a GUI program using dlangui. It has some checkboxes. I'm trying to figure out how to invoke a callback function when the user clicks the box. What are the valid ways of doing that?

I can copy from dlangide's source, where a delegate is defined in-line and assigned. That seems to work. But is that the only way?

    bool g_x = true;

    bool checkbox_b_clicked(Widget source, bool checked)
    {
      g_x = checked;
      if (checked) {
          writeln(checked);
      }
      return true;
    }


    auto check_a = new CheckBox("wantalt", "Alternating"d);
    auto check_b = new CheckBox("wantblinkb", "Blink(delg)"d);
    auto check_c = new CheckBox("wantblinkc", "Blink(direct)"d);

    check_a.checkChange = delegate(Widget w, bool checked) {
                 g_x=checked;
                 return true;
                 };
    check_b.checkChange = delegate(Widget w, bool checked) {
                 return checkbox_b_clicked(w,checked);
                 };
    check_c.checkChange = checkbox_b_clicked;
    check_c.checkChange = &checkbox_b_clicked;

The assignment to check_a is fine with the compiler.

For check_b, I try calling a function defined earlier. (Maybe in real life it's too complex to try having inline.) It was giving a compiler error until I realized I'm dumb, wasn't passing 'w' and 'checked' to it. Fixed, works fine now. Okay!

But what I think I should be able to do: assign checkbox_b_clicked directly to the .checkChange property of the checkbox, as shown for check_c. It doesn't work. Oh, I see an example where '&' is used - okay let's try that... nope!

The compiler errors I get are, for no '&' and with '&':

Error: function app.checkbox_b_clicked(Widget source, bool checked) is not callable using argument types ()

Error: none of the overloads of opAssign are callable using argument types (bool function(Widget source, bool checked))

On Saturday, 31 December 2022 at 02:40:49 UTC, Daren Scot Wilson wrote:

Try:

import std.functional : toDelegate;
check_c.checkChange = toDelegate(&checkbox_b_clicked);

On Saturday, 31 December 2022 at 03:05:45 UTC, brianush1 wrote:

import std.functional : toDelegate;
check_c.checkChange = toDelegate(&checkbox_b_clicked);

That works :)

On Saturday, 31 December 2022 at 02:40:49 UTC, Daren Scot Wilson wrote:

If checkbox_b_clicked is a non-static nested function or non-static method, taking the address of it should result in a delegate, not a function pointer.

You can check what it is like this:

writeln(typeid(&checkbox_b_clicked));