public class List<T>
{
public int Count
{
get;
}
}
I noticed Count is an int, will the result be less than 0？
If Count could be less than 0, I have to write that：
if(myList.Count < 1)
{
}
otherwise I can write that:
if(myList.Count == 0)
{
}
From the comments:
Just to be on the safe side, because I noticed the Count is a
intbut not auint
When the List<T> class was designed, Microsoft's .NET class library design rules meant that UInt32 (aka uint) could not be used for any public members, so instead Int32 (aka int) was used.
Count is an int (aka Int32) property instead of a uint (or UInt32) property is because the List<T> type was defined when the Common Language Specification (the "CLS") was still being respected by Microsoft.
Int32 is CLS-compliant.UInt32 is not CLS-compliant.Count was typed as UInt32 instead of Int32 then users of those other languages couldn't use List<T>.Count at all.List<T>.Count ever be negative or otherwise invalid?Provided you use a List<T> instance in a safe manner, then no, the .Count property will always return a value in the range 0 to 2^31 (the actual maximum count of a List<T> is a different question which is already answered here).
However, if you use a List<T> in a thread-unsafe manner (such as having 2 or more threads concurrently adding and removing items from a list without using lock correctly), or if you use tricks like reflection to override the .Count property's field value then yes, you can break things. So don't do that :)
The motivation for the CLS is described in this article:
- To enable full interoperability scenarios, all objects that are created in code must rely on some commonality in the languages that are consuming them (are their callers).
- Since there are numerous different languages, .NET has specified those commonalities in something called the Common Language Specification (CLS).
The Common Language Specification is described in this MSDN article, which has a list of types built-in to .NET but which are verboten for use in CLS-compliant frameworks and redistributable libraries.
System.SByte aka sbyte.
System.UInt16 aka ushort.System.UInt32 aka uint.System.UInt64 aka ulong.System.UIntPtr.Also:
- The rules for CLS compliance apply only to a component's public interface, not to its private implementation.
- For example, unsigned integers other than
Byteare not CLS-compliant [...].
No, the reference source (which only apply for .NET Framework) for that property is
public int Count {
get {
Contract.Ensures(Contract.Result<int>() >= 0);
return _size;
}
}
which due to how Contract.Ensures works, guarantee it will never return less than zero.
As for .NET Core, that property is simply
public int Count => _size;
_size itself can't ever get below zero according to all the assignments in the code.
Of course it can, why even ask. Here is some blasphemy:
[TestFixture]
public class TotalGarbageTests
{
[Test]
public void Blasphemy()
{
var list = new List<int>();
list.GetType().GetField("_size", BindingFlags.Instance | BindingFlags.NonPublic).SetValue(list, -666);
Assert.AreEqual(-666, list.Count);
}
}
PS Now you are probably corrupted by knowledge, but meh, whatever.
