scalacheck 中生成器的大小
scalacheck 项目的 UserGuide 提到了大小的生成器。解释代码
def matrix[T](g:Gen[T]):Gen[Seq[Seq[T]]] = Gen.sized {size =>
val side = scala.Math.sqrt(size).asInstanceOf[Int] //little change to prevent compile-time exception
Gen.vectorOf(side, Gen.vectorOf(side, g))
}
对我没有任何解释。经过一番探索后，我了解到生成序列的长度并不取决于生成器的实际大小（Gen 对象中有调整大小方法，根据 javadoc“创建生成器的调整大小版本”（也许这意味着不同的东西？））。
val g = Gen.choose(1,5)
val g2 = Gen.resize(15, g)
println(matrix(g).sample) // (1)
println(matrix(g2).sample) // (2)
//1,2 produce Seq with same length
您能否解释一下我错过了什么，并给我一些如何在测试代码中使用它们的示例？
UserGuide of scalacheck project mentioned sized generators. The explanation code
def matrix[T](g:Gen[T]):Gen[Seq[Seq[T]]] = Gen.sized {size =>
val side = scala.Math.sqrt(size).asInstanceOf[Int] //little change to prevent compile-time exception
Gen.vectorOf(side, Gen.vectorOf(side, g))
}
explained nothing for me. After some exploration I understood that length of generated sequence does not depend on actual size of generator (there is resize method in Gen object that "Creates a resized version of a generator" according to javadoc (maybe that means something different?)).
val g = Gen.choose(1,5)
val g2 = Gen.resize(15, g)
println(matrix(g).sample) // (1)
println(matrix(g2).sample) // (2)
//1,2 produce Seq with same length
Could you explain me what had I missed and give me some examples how you use them in testing code?
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vectorOf（现在已替换为listOf）生成的列表，其大小（线性）取决于 ScalaCheck 在计算生成器时设置的大小参数。当 ScalaCheck 测试属性时，它会为每个测试增加此大小参数，从而导致使用越来越大的列表来测试属性（如果使用listOf）。如果您仅通过以嵌套方式使用
listOf生成器来创建矩阵生成器，您将获得大小取决于大小参数的平方的矩阵。因此，当在属性中使用此类生成器时，您可能会得到非常大的矩阵，因为 ScalaCheck 会增加每次测试运行的大小参数。但是，如果您按照 ScalaCheck 用户指南中的方式使用resize生成器组合器，则最终矩阵大小线性取决于大小参数，从而在测试属性时获得更好的性能。您实际上不必经常使用
resize生成器组合器。如果您需要生成受某个特定大小限制的列表，最好执行如下示例所示的操作，因为不能保证listOf/containerOf生成器确实按照您期望的方式使用大小参数。The
vectorOf(which now is replaced withlistOf) generates lists with a size that depends (linearly) on the size parameter that ScalaCheck sets when it evaluates a generator. When ScalaCheck tests a property it will increase this size parameter for each test, resulting in properties that are tested with larger and larger lists (iflistOfis used).If you create a matrix generator by just using the
listOfgenerator in a nested fashion, you will get matrices with a size that depends on the square of the size parameter. Hence when using such a generator in a property you might end up with very large matrices, since ScalaCheck increases the size parameter for each test run. However, if you use theresizegenerator combinator in the way it is done in the ScalaCheck User Guide, your final matrix size depend linearly on the size parameter, resulting in nicer performance when testing your properties.You should really not have to use the
resizegenerator combinator very often. If you need to generate lists that are bounded by some specific size, it's much better to do something like the example below instead, since there is no guarantee that thelistOf/containerOfgenerators really use the size parameter the way you expect.您使用的
vectorOf方法已被弃用，您应该使用 listOf 方法。这会生成一个随机长度的列表，其中最大长度受生成器大小的限制。因此，您应该调整生成器的大小如果您想控制生成的最大元素，实际上会生成实际列表：
The
vectorOfmethod that you use is deprecated , and you should use the listOf method. This generates a list of random length where the maximum length is limited by the size of the generator. You should therefore resize the generator thatactually generates the actual list if you want control over the maximum elements that are generated: