Question

I was looking at the documentation for BigInteger and ran across the following in the BigInteger.Equals(Object obj) method:

If the obj parameter is not a BigInteger value, but it is a data type for which an implicit conversion is defined, the Equals(Object) method converts obj to a BigInteger value before it performs the comparison.

I then started wondering how I would go about doing this, given that converting from the object would require an explicit cast. The best way I came up with is as follows:

Type type = obj.GetType()
if(type == typeof(byte))
{
  byte b = (byte)obj;
  return Equals(b);
}
if(type == typeof(short))
{
  short s = (short)obj;
  return Equals(s);
}
//Continue for all types that can be implicitly cast to BigInteger.

It just seems to me that there’s an easier way to do this that I’m missing. So what other methods are there to do an implicit conversion, given that I’m starting with an object?

Answer 1

The current implementation from ILSpy:

return obj is BigInteger && this.Equals((BigInteger)obj);

At the very least the documentation could be considered misleading in its wording. What it means is BigInteger or anything that derives from it will have an implicit cast to BigInteger and will thus be cast to a BigInteger for the purposes of testing equality.

The current definition of struct will mean that nothing can derive from BigInteger, so the documentation is actually a little pointless in that statement.

It is possible you are getting confused with the user-defined implicit operator, which is what will have been used to allow int, short, et al to be stored in BigInteger “implicitly” in code:

BigInteger b = 1;