我在Visual Studio2010中创建了一个控制台项目,并选择了.Net Framework2.0
namespace ConsoleApp1
{
class Program
{
public int Add(int a, int b = 0, int c = 0)
{
Console.WriteLine("a is " + a);
Console.WriteLine("b is " + b);
Console.WriteLine("c is " + c);
retur
常识表明,对于返回类型,子类型应该是协变的,而对于参数类型,则应该是反变体。因此,由于E.f的严格协变参数类型,应该拒绝以下内容
interface C {
f (o: C): void
}
interface D extends C {
g (): void // give D an extra service
}
class E implements C {
// implement f with a version which makes stronger assumptions
f (o: D): void {
o.g() // rely on
我正在尝试为Arduino编译一个来自的例子。我得到了这个错误:
In file included from sha1test.pde:1:
C:\Program Files (x86)\Arduino\libraries\Sha/sha1.h:26: error: conflicting return type specified for 'virtual void Sha1Class::write(uint8_t)'
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino/Print.h:48: error
class B : A {}
class Sub<T> where T:A
{
//...
}
我想将Sub实例存储在一个集合中。
var c = new List<Sub<A>>();
c.Add(new Sub<B>()); //doesn't work
但是,为了让它真正工作,我必须声明一个接口并存储该接口的实例。
interface IBase
{
void DoStuff(A a);
}
var c = new List<IBase>();
c.Add(new Sub<B>()); //work