C#

List<string> remove = new List<string>();
foreach (KeyValuePair<sting, foo=""> item in dic) if (item.Value.order > 100) remove.Add(item.Key);
foreach (string key in remove) dic.Remove(key);</sting,>

George_George wrote:

In my original code, I am not foreach the whole Dictionary, just the .Keys of the Dictionary (i.e. using Keys Enumerator, not using Dictionary as a whole Enumerator). In this case, deleting an element will also invaliding the Keys Enumerator? Why?

foreach (var entry in dict.ToList())
    if(entry.Value.order > 100)
         dict.Remove(entry.Key);

class A
{
  public virtual void Message()
  {
     Console.WriteLine("Original Message");
  }
}

class B : A
{
  public new void Message()
  {
     Console.WriteLine("Class B's Message");
  }
}

class C : A
{
  public override void Message()
  {
     Console.WriteLine("Class C's Message");
  }
}

A myA = new A();
B myB = new B();
C myC = new C();

myA.Message(); //Outputs "Original Message"
myB.Message(); //Outputs "Class B's Message"
myC.Message(); //Outputs "Class C's Messgae"

//Notice that these are of type A
A myAB = new B(); 
A myAC = new C();

myAB.Message(); //Outputs "Original Message"
myAC.Message(); //Outputs "Class C's Message"

George_George wrote:

If I call remove method to remove some elements from the Dictionary, will the memory footprint be reduced? (suppose there is no other reference to the removed item) I have some suspecision that Dictionary is not truly removing the element and just mark a flag or something, which still refer this removed item to block it from GCed.

George_George wrote:

The other is to create a new Dictionary instance, and insert only necessary items into the new Dictionary instance, and reference only the new Dictionary instance in the future.

George_George wrote:

Which way is better from memory footprint reduce perspective?

George_George wrote:

I do not quite understand "the key value pair is cleared, but kept", kept for what? I think the word clear is conflicting to "kept".

George_George wrote:

Could you provide more descriptions about why based on the above theory, reference types are cleared from memory, but value types are not?

George_George wrote:

I think when insert value types into Dictionary, it will be value copied, right?