在 Objective-C 中，可以向他们的类添加一个description方法来帮助调试：

@implementation MyClass
- (NSString *)description
{
    return [NSString stringWithFormat:@"<%@: %p, foo = %@>", [self class], foo _foo];
}
@end

然后在调试器中，您可以执行以下操作：

po fooClass
<MyClass: 0x12938004, foo = "bar">

Swift 中的等价物是什么？Swift 的 REPL 输出可能会有所帮助：

  1> class MyClass { let foo = 42 }
  2> 
  3> let x = MyClass()
x: MyClass = {
  foo = 42
}

但我想覆盖此行为以打印到控制台：

  4> println("x = \(x)")
x = C11lldb_expr_07MyClass (has 1 child)

有没有办法清理这个println输出？我看过Printable协议：

/// This protocol should be adopted by types that wish to customize their
/// textual representation.  This textual representation is used when objects
/// are written to an `OutputStream`.
protocol Printable {
    var description: String { get }
}

我认为这会自动被“看到”，println但似乎并非如此：

  1> class MyClass: Printable {
  2.     let foo = 42
  3.     var description: String { get { return "MyClass, foo = \(foo)" } }
  4. }   
  5> 
  6> let x = MyClass()
x: MyClass = {
  foo = 42
}
  7> println("x = \(x)")
x = C11lldb_expr_07MyClass (has 1 child)

相反，我必须明确调用描述：

 8> println("x = \(x.description)")
x = MyClass, foo = 42

有没有更好的办法？