scala – “No Manifest available for Type”错误

abstract class A { var a : Int = _}
class B[T] extends A { var b : T = _ }
class C[T] extends A { var c : T = _ }
class Abc[T : Manifest] {
    var array : Array[T] = _
    def this(capacity : Int,f : Unit => T) = {
        this()
        array = new Array[T](capacity)
        for(i <- 0 until capacity)
            array(i) = f()
    }
}

class Xyz[T] { 
    var m : Abc[C[T]] = _; 
    def this(capacity : Int) = { 
    this(); 
    m = new Abc[C[T]](capacity,Unit => { new C[T]() })
    }
}

var xyz = new Xyz[Int](10)

但我得到了：

error: No Manifest available for C[T].
       class Xyz[T] { var m : Abc[C[T]] = _; def this(capacity : Int) = { this(); m = new Abc[C[T]](capacity,Unit => { new C[T]() })}}
                                                                                      ^

据我所知,我需要为lambda函数设置隐式Manifest参数

Unit => { new C[T]() })

但是我该怎么做呢？或者我完全错了？