有没有办法在swift中打印一个变量的运行时类型？例如：
var Now = NSDate()
var soon = Now.dateByAddingTimeInterval(5.0)
println("\(Now.dynamicType)")
// Prints "(Metatype)"
println("\(Now.dynamicType.description()")
// Prints "__NSDate" since objective-c Class objects have a "description" selector
println("\(soon.dynamicType.description()")
// Compile-time error since ImplicitlyUnwrappedOptional<NSDate> has no "description" method
在上面的例子中，我正在寻找一种方法来显示变量“soon”的类型ImplicitlyUnwrappedOptional，或至少NSDate！。
2016年9月更新
Swift 3.0：使用类型(of :)，例如type(of：someThing)(因为dynamicType关键字已被删除)
2015年10月更新：
我更新了下面的例子到新的Swift 2.0语法(例如println被替换为print，toString()现在是String())。
从Xcode 6.3发行说明：
@nschum指出在Xcode 6.3 release notes显示另一种方式的意见：
Type values Now print as the full demangled type name when used with
println or string interpolation.
import Foundation
class PureSwiftClass { }
var myvar0 = Nsstring() // Objective-C class
var myvar1 = PureSwiftClass()
var myvar2 = 42
var myvar3 = "Hans"
print( "String(myvar0.dynamicType) -> \(myvar0.dynamicType)")
print( "String(myvar1.dynamicType) -> \(myvar1.dynamicType)")
print( "String(myvar2.dynamicType) -> \(myvar2.dynamicType)")
print( "String(myvar3.dynamicType) -> \(myvar3.dynamicType)")
print( "String(Int.self) -> \(Int.self)")
print( "String((Int?).self -> \((Int?).self)")
print( "String(Nsstring.self) -> \(Nsstring.self)")
print( "String(Array<String>.self) -> \(Array<String>.self)")
其中输出：
String(myvar0.dynamicType) -> __NSCFConstantString String(myvar1.dynamicType) -> PureSwiftClass String(myvar2.dynamicType) -> Int String(myvar3.dynamicType) -> String String(Int.self) -> Int String((Int?).self -> Optional<Int> String(Nsstring.self) -> Nsstring String(Array<String>.self) -> Array<String>
更新Xcode 6.3：
您可以使用_stdlib_getDemangledTypeName()：
print( "TypeName0 = \(_stdlib_getDemangledTypeName(myvar0))") print( "TypeName1 = \(_stdlib_getDemangledTypeName(myvar1))") print( "TypeName2 = \(_stdlib_getDemangledTypeName(myvar2))") print( "TypeName3 = \(_stdlib_getDemangledTypeName(myvar3))")
并将其作为输出：
TypeName0 = Nsstring TypeName1 = __lldb_expr_26.PureSwiftClass TypeName2 = Swift.Int TypeName3 = Swift.String
原始答案：
在Xcode 6.3之前_stdlib_getTypeName获取变量的受损类型名称。 Ewan Swick’s blog entry帮助解密这些字符串：
例如_TtSi代表Swift的内部Int类型。
Mike Ash has a great blog entry covering the same topic。