c# - 将方法参数验证代码重构为Contracts - 语句反转问题

Question

旧的验证代码通常检查 bool 条件，如果条件为真则抛出异常。

相反，Contract.Requires(...) 做相反的事情(为了通过检查，我们需要否定旧条件)。

我正在重构旧代码，有时会看到一些相当高级的 bool 语句，反转它们并不是那么容易，只是做 Contract.Requires(!(*old statements*)) 看起来很糟糕并且非常困惑。

如果它有类似 Contract.RequiresNot() 的东西，重构在这里会更加清晰和直接。

我们也不能添加静态扩展方法。如果有人遇到这个问题并找到了一些好的解决方案，我很想听听。

Answer 1

您可以尝试保留旧的遗留验证并添加 Contract.EndContractBlock验证后立即调用。来自 MSDN:

Most code contains some parameter validation in the form of if-then-throw code. The contract tools recognize these statements as preconditions in the following cases:

• The statements appear before any other statements in a method.
• The entire set of such statements is followed by an explicit Contract method call, such as a call to the Requires, Ensures, EnsuresOnThrow, or EndContractBlock method.

When if-then-throw statements appear in this form, the tools recognize them as legacy requires statements. If no other contracts follow the if-then-throw sequence, end the code with the Contract.EndContractBlock method.

if ( x == null ) throw new ...
Contract.EndContractBlock(); // All previous "if" checks are preconditions

Note that the condition in the preceding test is a negated precondition. (The actual precondition would be x != null.) A negated precondition is highly restricted: It must be written as shown in the previous example; that is, it should contain no else clauses, and the body of the then clause must be a single throw statement. The if test is subject to both purity and visibility rules (see Usage Guidelines), but the throw expression is subject only to purity rules. However, the type of the exception thrown must be as visible as the method in which the contract occurs.