C#

George_George wrote:

For value type, even if we provide a customized constructor, there is also the default one (co-exist with customized one)?

George_George wrote:

For reference type, there is also a default constructor even if we provide a customized one (co-exist with default one)?

ForumExpertOnLine wrote:

George_George wrote:
For value type, even if we provide a customized constructor, there is also the default one (co-exist with customized one)?

NO

struct S
{
    int x;
    public S(int x)
    {
        this.x = x;
    }

    public int X
    {
        get { return x; }
    }
}
class Program
{
    static void Main(string[] args)
    {
        S s = new S();
        Console.WriteLine(s.X);
    }
}

George_George wrote:

1. For value type, whether or not we provide a customized constructor, there is a default one (co-exist with customized one).

George_George wrote:

2. For reference type, there is also a default constructor, whether or not we provide a customized one (co-exist with default one).

George_George wrote:

I think for value types, only the memory space is reserved, you can not access the fields if you only "create" them with default constructor and not initializing to them. Right?

struct Foo
{
    public int abc;
}

George_George wrote:

For code like this,

struct Foo
{
public int abc;
}

Is there a default constructor generated which is parameter-less?

L_0000: ldloca.s x<br />
L_0002: initobj Foo

Guffa wrote:

George_George wrote:
1. For value type, whether or not we provide a customized constructor, there is a default one (co-exist with customized one).



No,

S. Senthil Kumar wrote:

Actually yes, there is always the default parameterless constructor, regardless of whether you overload it or not.

George_George wrote:

1. For value type, even if we provide a customized constructor, there is also the default one (co-exist with customized one)?

George_George wrote:

2. For reference type, there is also a default constructor even if we provide a customized one (co-exist with default one)?

S. Senthil Kumar wrote:

"If no instance constructor is supplied for a class, then an empty one with no parameters is automatically provided."

George_George wrote:

And even if we provide a customized one, the default parameter-less one still exists.

class S
{
    int x;
    public S(int x)
    {
        this.x = x;
    }

    public int X
    {
        get { return x; }
    }
}
class Program
{
    static void Main(string[] args)
    {
        S s = new S();
        Console.WriteLine(s.X);
    }
}

StructValueType abc;

George_George wrote:

the memory for new instance of abc is actually allocated even if we do not use new + constructor explicitly

George_George wrote:

StructValueType abc;

George_George wrote:

So, for statement like below, the memory for new instance of abc is actually allocated even if we do not use new + constructor explicitly. But for reference type, without using new, no instances' space are allocated. Correct?

S. Senthil Kumar wrote:

so stack space will be reserved right away.

George_George wrote:

And even if we provide a customized one, the default parameter-less one still exists.

class Program
{
   static void Main(string[] args)
   {
      Foo foo = new Foo();
   }
}
class Foo
{
   public Foo(int param)
   {
   }
}