CODEWITHSUNDEEP
c#
Roman Ratskey
Roman Ratskey

Reputation: 5269

How are typeof and sizeof Implemented

I want to know how the typeof and sizeof keywords are implemented.

What if I want to implement my own 'x'of() expression like timeof(object) where object contains a DateTime as one of it's properties or something?

Upvotes: 5

Views: 198

Answers (2)

Tim S.
Tim S.

Reputation: 56556

The short answer is no. typeof and sizeof are part of the C# language, and you cannot (directly) add expressions like them. The normal way of doing what you're asking would be to simply access the property:

DateTime time = myObject.SomeDateTimeProperty;

You could make a method to do this (although it wouldn't make sense for such a trivial thing). E.g. if you used an interface:

public interface ICreateTime
{
    DateTime CreateTime { get; }
}

public DateTime TimeOf(ICreateTime myObject)
{
    return myObject.CreateTime;
}

To be more specific: typeof and sizeof aren't implemented in the same way you implement methods. Instead, typeof translates to ldtoken [type] and call System.Type.GetTypeFromHandle IL instructions, and sizeof becomes a constant. E.g.

Type t = typeof(int);
int s = sizeof(int);

Compiles to:

IL_0001:  ldtoken     System.Int32
IL_0006:  call        System.Type.GetTypeFromHandle
IL_000B:  stloc.0     // t
IL_000C:  ldc.i4.4    // the constant 4, typed as a 4-byte integer
IL_000D:  stloc.1     // s

Upvotes: 10

Soturi
Soturi

Reputation: 1496

For your use case, I would not recommend doing this even if it was possible.

typeof and sizeof are both methods that return information relevant to the compiler. Getting the time of an object is accessing a property and not a compiler attribute.

If you have an object that has a DateTime you should be accessing it using:

object.DateTimeProperty

Upvotes: 1

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