如何指示方法永远不会使用代码契约返回null？

Question

如何指示方法永远不会返回null？目前这是我的代码.

第19行获得了一个Ensures未经验证的消息,即使CreateFunction假定结果不是什么.

1         <Pure()> Public Function CreateFunction(Of TArg1, TArg2, TResult)(ByVal body As Func(Of Expression, Expression, BinaryExpression)) As Func(Of TArg1, TArg2, TResult)   
2             Contract.RequiresAlways(body IsNot Nothing)   
3             Contract.Assume(Contract.Result(Of Func(Of TArg1, TArg2, TResult))() IsNot Nothing)   
4   
5             Dim arg1 = Expression.Parameter(GetType(Integer), "arg1")   
6             Dim arg2 = Expression.Parameter(GetType(Integer), "arg2")   
7   
8   
9             Dim temp = Expression.Lambda(body(arg1, arg2), arg1, arg2)   
10             Contract.Assume(temp IsNot Nothing)   
11             Return DirectCast(temp.Compile, Global.System.Func(Of TArg1, TArg2, TResult))   
12         End Function  
13   
14         <Pure()> Public Function Add() As Func(Of T, T, T)   
15             Contract.Ensures(Contract.Result(Of Func(Of T, T, T))() IsNot Nothing)   
16   
17             Dim temp = CreateFunction(Of T, T, T)(AddressOf Expression.AddChecked)   
18             Return temp   
19         End Function  

Answer 1

是否

Contract.Ensures(Contract.Result() != null);

工作？基本上,我会尝试将它削减,直到你发现最简单的情况不会像你期望的那样工作并从那里开始.

- MarkusQ