$and, $or, $is_const, $assignable, .is_eq, .is_ordered, $defined($vatype(2)) works looking if we can create a type, $defined(foo[0]) $defined(foo()). Remove $checks and @checked. Improvide casting checks to always work without destructive changes.

test/unit/regression/castable_assignable.c3

@@ -0,0 +1,24 @@
+module castable @test;
+
+fn void assignable()
+{
+	assert($assignable(12.0, int) == false);
+	assert($assignable(12, int));
+	assert(!$assignable("12", int));
+	assert($assignable("12", String));
+	assert($assignable("12", char*));
+	assert($assignable("12", char[*]));
+	assert($assignable("12", char[2]));
+	assert($assignable("12", char[3]));
+}
+
+fn void castable()
+{
+	assert($defined((int)12.0));
+	assert($defined((int)12));
+	assert(!$defined((int)"12"));
+	assert($defined((String)"12"));
+	assert($defined((char*)"12"));
+	assert($defined((char[2])"12"));
+	assert($defined((char[3])"12"));
+}