把类型强制转换当作一种断言，把不变量当做说明该断言为true的原因的参数。

Think of a cast as a kind of assertion and the invariants as arguments for why the assertion is true.

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最后，不变条件测试断言永远不变的条件。

Finally, invariant tests assert conditions that never change.

youdao

最后，不变条件测试断言永远不变的条件。

Finally, invariant tests assert conditions that never change.

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