scala - 为什么添加括号会改变这个 Scala 表达式的结果？

Question

我正在将一些 C 代码移植到 Scala，它广泛使用了浮点运算。我根据 C 版本的复制/粘贴在 Scala 中编写了以下代码:

val complimentaryTerms = 2640.96e-6 * sin (f5)
          +  63.52e-6 * sin (2.0 * f5)
          +  11.75e-6 * sin (2.0 * f3 - 2.0 * f4 + 3.0 * f5)
          +  11.21e-6 * sin (2.0 * f3 - 2.0 * f4 +       f5)
          -  4.55e-6 * sin (2.0 * f3 - 2.0 * f4 + 2.0 * f5)
          +  2.02e-6 * sin (2.0 * f3            + 3.0 * f5)
          +  1.98e-6 * sin (2.0 * f3            +       f5)
          -  1.72e-6 * sin (3.0 * f5)
          -  0.87e-6 * t * sin (f5)

此计算的结果与 C 版本产生的结果略有不同。但是，如果我将表达式括在括号中，如下所示:

val complimentaryTerms = (2640.96e-6 * sin (f5)
          +  63.52e-6 * sin (2.0 * f5)
          +  11.75e-6 * sin (2.0 * f3 - 2.0 * f4 + 3.0 * f5)
          +  11.21e-6 * sin (2.0 * f3 - 2.0 * f4 +       f5)
          -  4.55e-6 * sin (2.0 * f3 - 2.0 * f4 + 2.0 * f5)
          +  2.02e-6 * sin (2.0 * f3            + 3.0 * f5)
          +  1.98e-6 * sin (2.0 * f3            +       f5)
          -  1.72e-6 * sin (3.0 * f5)
          -  0.87e-6 * t * sin (f5))

结果值与 C 版本完全匹配。当有括号时和没有括号时，运算顺序似乎必须不同，但我不明白为什么这会产生任何差异。知道这里发生了什么吗？

Answer 1

这是因为分号推断。示例(//; - 推断的分号):

val x = 1 //;
        + 1 //;
println(x) // 1

带括号:

val x = (1
        + 1) //;
println(x) // 2

或者带尾部“+”:

val x = 1 +
        1 //;
println(x) // 2

The rules of semicolon inference
A line ending is treated as a semicolon unless one of the following conditions is true:

1. The line in question ends in a word that would not be legal as the end of a statement, such as a period or an infix operator.

2. The next line begins with a word that cannot start a statement.

3. The line ends while inside parentheses (...) or brackets [...], because these cannot contain multiple statements anyway.