对象字段的默认值

对象字段允许具有一个常量默认值。如果提供了默认值，则可以省略字段的类型。

  1. type
  2.   Foo = object
  3.     a: int = 2
  4.     b: float = 3.14
  5.     c = "I can have a default value"
  7.   Bar = ref object
  8.     a: int = 2
  9.     b: float = 3.14
  10.     c = "I can have a default value"

显式初始化使用这些默认值，包括使用对象构造表达式或过程 default 创建的 object ；使用对象构造表达式或过程 new 创建的 ref object ；具有子类型的数组或元组，该子类型使用过程 default 创建了默认值。

  1. type
  2.   Foo = object
  3.     a: int = 2
  4.     b = 3.0
  5.   Bar = ref object
  6.     a: int = 2
  7.     b = 3.0
  9. block: # created with an object construction expression
  10.   let x = Foo()
  11.   assert x.a == 2 and x.b == 3.0
  13.   let y = Bar()
  14.   assert y.a == 2 and y.b == 3.0
  16. block: # created with an object construction expression
  17.   let x = default(Foo)
  18.   assert x.a == 2 and x.b == 3.0
  20.   let y = default(array[1, Foo])
  21.   assert y[0].a == 2 and y[0].b == 3.0
  23.   let z = default(tuple[x: Foo])
  24.   assert z.x.a == 2 and z.x.b == 3.0
  26. block: # created with the procedure `new`
  27.   let y = new Bar
  28.   assert y.a == 2 and y.b == 3.0