From d2f542ffeecddf36004f94729745e4ba9d7d300a Mon Sep 17 00:00:00 2001
From: Dan Liew <daniel.liew@imperial.ac.uk>
Date: Thu, 12 Feb 2015 11:04:51 +0000
Subject: When an Expr immutable, never change Type reference if it has been
 set, even if the types are equivalent.

---
 Source/Core/AbsyExpr.cs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

(limited to 'Source/Core/AbsyExpr.cs')

diff --git a/Source/Core/AbsyExpr.cs b/Source/Core/AbsyExpr.cs
index 3938e396..7557a796 100644
--- a/Source/Core/AbsyExpr.cs
+++ b/Source/Core/AbsyExpr.cs
@@ -104,7 +104,10 @@ namespace Microsoft.Boogie {
           if (Immutable && !_Type.Equals(value))
             throw new InvalidOperationException("Cannot change the Type of an Immutable Expr");
 
-          _Type = value;
+          // Once the Type has been set (i.e. no longer null) we never change the reference 
+          // if this Expr is immutable, even if the Type is equivalent (i.e. _Type.Equals(newType))
+          if (!Immutable)
+            _Type = value;
         }
       }
     }
-- 
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