与断言相比，scala中的假设是什么意思? [英] What is the meaning of an assumption in scala compared to an assertion?

问题描述

Scala似乎定义了3种断言:assert，require和assume.

Scala seems to define 3 kinds of assertions: assert, require and assume.

据我了解，require的区别(与一般断言相比)是它专门用于检查输入(参数，传入消息等).那么assume的含义是什么?

As far as I can understand, the difference (compared to a generic assertion) of require is that it is specifically meant for checking inputs (arguments, incoming messages etc). And what's the meaning of assume then?

推荐答案

如果查看Predef.scala中的代码，您会发现这三个代码都做得非常相似:

If you look at the code in Predef.scala you'll see that all three do very similar job:

def assert(assertion: Boolean) { 
  if (!assertion) 
    throw new java.lang.AssertionError("assertion failed") 
} 

def assume(assumption: Boolean) { 
  if (!assumption) 
    throw new java.lang.AssertionError("assumption failed") 
} 

def require(requirement: Boolean) { 
  if (!requirement) 
    throw new IllegalArgumentException("requirement failed") 
} 

还有一些版本出于报告目的采用了额外的参数(请参见 http://harrah.github.com/browse/samples/library/scala/Predef.scala.html ).

There are also versions which take extra arguments for reporting purposes (see http://harrah.github.com/browse/samples/library/scala/Predef.scala.html).

区别在于它们引发的异常类型和它们生成的错误消息.

The difference is in the exception type they throw and error message they generate.

但是，静态检查器可以对所有这三个方法进行不同的处理.目的是让assert指定一个条件，该条件应尝试进行静态检查，而assume将用于确定检查者可能认为要保持的条件，而require则指定调用者必须确保的条件. .如果静态检查者发现违反assert的行为，则认为它是代码中的错误，而当违反require的行为时，则认为调用者有错误.

However, static checkers could treat all three differently. The intention is for assert to specify a condition that a static check should attempt to prove, assume is to be used for a condition that the checker may assume to hold, while require specifies a condition that the caller must ensure. If a static checker finds a violation of assert it considers it an error in the code, while when require is violated it assumes the caller is at fault.

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