py: Implement implicit cast to obj for viper load/store index/value.

This allows to do "ar[i]" and "ar[i] = val" in viper when ar is a Python
object and i and/or val are native viper types (eg ints).

Patch also includes tests for this feature.

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/micropython/viper_subscr.py b/tests/micropython/viper_subscr.py
new file mode 100644
index 000000000..2198ed731
--- /dev/null
+++ b/tests/micropython/viper_subscr.py
@@ -0,0 +1,20 @@
+# test standard Python subscr using viper types
+
+@micropython.viper
+def get(dest, i:int):
+    i += 1
+    return dest[i]
+
+@micropython.viper
+def set(dest, i:int, val:int):
+    i += 1
+    dest[i] = val + 1
+
+ar = [i for i in range(3)]
+
+for i in range(len(ar)):
+    set(ar, i - 1, i)
+print(ar)
+
+for i in range(len(ar)):
+    print(get(ar, i - 1))