vala consumes expressions like this:
const Demo[] testgtk_demos =
{
	{ "Application main window", "appwindow.c", do_appwindow, null }, 
	{ "Assistant", "assistant.c",     do_assistant,     null }, 
	{ "Entry", null, null, children}
};

const Demo[] children =
{
	{ "Entry Buffer",     "entry_buffer.c",     do_assistant, null },
	{ "Entry Completion", "entry_completion.c", do_assistant, null },
	{ "Search Entry",     "search_entry.c",     do_assistant, null }
};

but it displays errors:
** (valac:5773): CRITICAL **: vala_ccode_function_add_declaration: assertion `self != NULL' failed
** (valac:5773): CRITICAL **: vala_ccode_function_add_assignment: assertion `self != NULL' failed

when I try to feed it with this:

const Demo[] testgtk_demos =
{
	{ "Application main window", "appwindow.c", do_appwindow, null }, 
	{ "Assistant", "assistant.c", do_assistant, null }, 
	{ "Entry", null, null,
		{
			{ "Entry Buffer", "entry_buffer.c", do_assistant, null },
			{ "Entry Completion", "entry_completion.c", do_assistant, null },
			{ "Search Entry", "search_entry.c", do_assistant, null }
		}
	}
};