Contract code error? The order of elements in an expression in a general method and value types

Question

Consider the following code compiled using static analysis of code contracts:

void TestGood<T>(T arg) { Contract.Requires(arg != null); } void TestBad<T>(T arg) { Contract.Requires(null != arg); } void RunTest() { TestGood(Guid.Empty); // No warnings TestBad(Guid.Empty); // Warning - "CodeContracts: requires unproven: null != arg" } 

It seems that the order of the parameters in binary == important, which does not make much sense.

It is not limited to the type of Guid . For example, struct MyStruct { } gives the same behavior.

Oddly enough, if we pass a built-in numeric type (for example, the value is int 0 ), there will be no warning.

So the questions are:

• Is there a reason why calling TestBad gives a warning?
• If not, is this a bug in a static analyzer with a code contract?

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Using contract code version 1.5.60502.11 with Visual Studio 2012. Here is a screenshot showing the settings used . In addition, as I said, I asked the same question in the code contract with the user forum .