[Go] Add an example for goin and godirectorin

Shows how to use a go directory for passing an NULL terminated argv type
array.

This also exercises the bug in the previous commit.  That's why the
call1 function isn't assigned to zero, that the only case where that bug
happens.

Signed-off-by: Corey Minyard <cminyard@mvista.com>

Examples/go/goin/example.i

@@ -0,0 +1,106 @@
+
+%module(directors="1") example
+
+%inline %{
+// Helper functions for converting string arrays
+#include <stdlib.h>
+void *alloc_ptr_array(unsigned int len)
+{
+    return calloc(len, sizeof(void *));
+}
+void set_ptr_array(void *ain, unsigned int pos, void *val)
+{
+    void **a = (void **) ain;
+    a[pos] = val;
+}
+void *get_ptr_array(void *ain, unsigned int pos)
+{
+    void **a = (void **) ain;
+    return a[pos];
+}
+void free_ptr_array(void *ain)
+{
+    void **a = (void **) ain;
+    unsigned int i;
+
+    if (!a)
+        return;
+    for (i = 0; a[i]; i++) {
+        free(a[i]);
+    }
+    free(a);
+}
+char *uintptr_to_string(void *in)
+{
+    return (char *) in;
+}
+void *string_to_uintptr(char *in)
+{
+    return strdup(in);
+}
+%}
+
+// These typemaps convert between an array of strings in Go and a
+// const char** that is NULL terminated in C++.
+%typemap(gotype) (const char * const *) "[]string";
+%typemap(imtype) (const char * const *) "uintptr";
+%typemap(goin) (const char * const *) {
+	if $input == nil || len($input) == 0 {
+		$result = 0
+	} else {
+		$result = Alloc_ptr_array(uint(len($input) + 1))
+		defer func() {
+			Free_ptr_array($result)
+		}()
+		var i uint
+		for i = 0; i < uint(len($input)); i++ {
+			Set_ptr_array($result, i, String_to_uintptr($input[i]))
+		}
+	}
+}
+%typemap(in) (const char * const *) {
+    $1 = (char **) $input;
+}
+%typemap(godirectorin) (const char * const *) {
+	if ($input == 0) {
+		$result = nil
+	} else {
+		var i uint
+		for i = 0; ; i++ {
+			var v uintptr = Get_ptr_array($input, i)
+			if v == 0 {
+				break
+			}
+		}
+		if i == 0 {
+			$result = nil
+		} else {
+			$result = make([]string, i)
+			for i = 0; ; i++ {
+				var v uintptr = Get_ptr_array($input, i)
+				if v == 0 {
+					break
+				}
+				$result[i] = Uintptr_to_string(v)
+			}
+		}
+	}
+}
+
+%feature("director") callbacks;
+
+%inline %{
+    class callbacks {
+    public:
+	virtual bool call1(int v, const char * const *strarray);
+	virtual ~callbacks() {}
+    };
+
+    bool check1(callbacks *c, int v, const char * const *strarray) {
+	return c->call1(v, strarray);
+    }
+
+    bool callbacks::call1(int v, const char * const *strarray) {
+        return false;
+    }
+%}