System.Array in c#

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4.00/5 (2 votes)

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I m amazed by seeing arrays implementation in c#.
int[] arr=new int[2];
how 'arr' shows methods and properties of System.Array class?.

I know System.Array class is instantiated internally by only compiler we can not explicitly instantiate it.

But again a.GetType().Name shows int[] type.ie a holds reference to array as well as System.Array class at a time ??

Posted 18-Oct-12 22:29pm

fdiu

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CPallini · Accepted Answer · 2012-10-18T22:54:00

Solution 1

As far as I know, arrays are System.Arrays. Or, as better stated by the documentation documentation[^]:
The Array class is the base class for language implementations that support arrays.

You may use ildasm[^] tool for inspecting generated code and verify yourself.

Posted 18-Oct-12 22:54pm

CPallini

Comments

fdiu 19-Oct-12 5:41am

But when we access int[2,2] then
in System.Array their is no implementation for indexer with two parameters.Then how its value come from??

fjdiewornncalwe 25-Oct-12 11:37am

+5. Good explanation.

CPallini 25-Oct-12 13:18pm

Thank you.

OriginalGriff · Accepted Answer · 2012-10-18T22:54:00

int[x] is syntactic sugar for System.Array(x) with an added "int" thrown in.
System.Array is an abstract class that is the base for all array datatypes in C#, it is just that you declare it using C# specific language constructs.

"But when we access int[2,2] then
in System.Array their is no implementation for indexer with two parameters.Then how its value come from??"

If you create a simple program:

C#

class Program
    {
    static void Main(string[] args)
        {
        int[,] arr = new int[2, 3];
        }
    }

And examine the EXE with ILDASM:

.method private hidebysig static void  Main(string[] args) cil managed
{
  .entrypoint
  // Code size       10 (0xa)
  .maxstack  2
  .locals init (int32[0...,0...] V_0)
  IL_0000:  nop
  IL_0001:  ldc.i4.2
  IL_0002:  ldc.i4.3
  IL_0003:  newobj     instance void int32[0...,0...]::.ctor(int32,
                                                             int32)
  IL_0008:  stloc.0
  IL_0009:  ret
} // end of method Program::Main

You will see that a constructor is defined for two dimensional arrays.
In all probability it is actually defined as params int[] dimensions to allow for two dimensional, three dimensional, and so on.

"Good,I think this is an constructor for System.Array(params int[])
But my question is actually this,

int i=a[2,2];
then here a[2,2] return an integer value.
But System.Array not contain indexer with two parameters so how it returns value.Then how it comes"

Again, the solution is to look at it with ILDASM:

C#

class Program
    {
    static void Main(string[] args)
        {
        int[,] arr = new int[4, 5];
        arr[2, 3] = 7;
        }
    }

.method private hidebysig static void  Main(string[] args) cil managed
{
  .entrypoint
  // Code size       19 (0x13)
  .maxstack  4
  .locals init (int32[0...,0...] V_0)
  IL_0000:  nop
  IL_0001:  ldc.i4.4
  IL_0002:  ldc.i4.5
  IL_0003:  newobj     instance void int32[0...,0...]::.ctor(int32,
                                                             int32)
  IL_0008:  stloc.0
  IL_0009:  ldloc.0
  IL_000a:  ldc.i4.2
  IL_000b:  ldc.i4.3
  IL_000c:  ldc.i4.7
  IL_000d:  call       instance void int32[0...,0...]::Set(int32,
                                                           int32,
                                                           int32)
  IL_0012:  ret
} // end of method Program::Main

Again, I would suspect a params parameter to the Set method.

And a similar result for the Get method:

C#

class Program
    {
    static void Main(string[] args)
        {
        int[,] arr = new int[4, 5];
        arr[2, 3] = 7;
        int i = arr[2, 3];
        }
    }

.method private hidebysig static void  Main(string[] args) cil managed
{
  .entrypoint
  // Code size       28 (0x1c)
  .maxstack  4
  .locals init ([0] int32[0...,0...] arr,
           [1] int32 i)
  IL_0000:  nop
  IL_0001:  ldc.i4.4
  IL_0002:  ldc.i4.5
  IL_0003:  newobj     instance void int32[0...,0...]::.ctor(int32,
                                                             int32)
  IL_0008:  stloc.0
  IL_0009:  ldloc.0
  IL_000a:  ldc.i4.2
  IL_000b:  ldc.i4.3
  IL_000c:  ldc.i4.7
  IL_000d:  call       instance void int32[0...,0...]::Set(int32,
                                                           int32,
                                                           int32)
  IL_0012:  ldloc.0
  IL_0013:  ldc.i4.2
  IL_0014:  ldc.i4.3
  IL_0015:  call       instance int32 int32[0...,0...]::Get(int32,
                                                            int32)
  IL_001a:  stloc.1
  IL_001b:  ret
} // end of method Program::Main