From e405170248f8b4d20fd0a3926dccdb850cb86660 Mon Sep 17 00:00:00 2001
From: Hang Su <hang.su@algorand.com>
Date: Fri, 21 Oct 2022 14:39:18 -0400
Subject: [PATCH] type cast init commit

---
 pyteal/ast/abi/util.py | 47 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/pyteal/ast/abi/util.py b/pyteal/ast/abi/util.py
index 4cece8b49..017ff4716 100644
--- a/pyteal/ast/abi/util.py
+++ b/pyteal/ast/abi/util.py
@@ -9,6 +9,7 @@
     get_args,
     get_origin,
 )
+from inspect import isabstract
 
 import algosdk.abi
 
@@ -593,3 +594,49 @@ def type_spec_is_assignable_to(a: TypeSpec, b: TypeSpec) -> bool:
         return True
 
     return False
+
+
+def type_cast_admissible(a: TypeSpec, b: TypeSpec) -> bool:
+    from pyteal.ast.abi import (
+        TupleTypeSpec,
+        StaticArrayTypeSpec,
+        DynamicArrayTypeSpec,
+    )
+
+    match a, b:
+        case TupleTypeSpec(), TupleTypeSpec():
+            a, b = cast(TupleTypeSpec, a), cast(TupleTypeSpec, b)
+            if a.length_static() != b.length_static():
+                return False
+
+            return all(
+                map(
+                    lambda ab: type_spec_is_assignable_to(ab[0], ab[1]),
+                    zip(a.value_type_specs(), b.value_type_specs()),
+                )
+            )
+        case DynamicArrayTypeSpec(), DynamicArrayTypeSpec():
+            a, b = cast(DynamicArrayTypeSpec, a), cast(DynamicArrayTypeSpec, b)
+            return type_cast_admissible(a.value_spec, b.value_spec)
+        case StaticArrayTypeSpec(), StaticArrayTypeSpec():
+            a, b = cast(StaticArrayTypeSpec, a), cast(StaticArrayTypeSpec, b)
+            return a.length_static() == b.length_static() and type_cast_admissible(
+                a.value_spec, b.value_spec
+            )
+        case _:
+            return type_spec_is_assignable_to(a, b)
+
+
+def type_cast(value: BaseType, t: type[T]) -> T:
+    if isabstract(t) or not issubclass(t, BaseType):
+        raise TealInputError(
+            f"type cast target class {t} cannot be abstract, and it has to be BaseType"
+        )
+    value_ts: TypeSpec = value.type_spec()
+    target_ts: TypeSpec = type_spec_from_annotation(t)
+
+    if not type_cast_admissible(value_ts, target_ts):
+        raise TealInputError(f"casting {value_ts} to {target_ts} is not allowed")
+    new_instance = target_ts.new_instance()
+    new_instance.stored_value.slot = value.stored_value.slot
+    return cast(T, new_instance)