C#

George_George wrote:

And we are free (allowed) to change the content (mmber fields) of object pointed by the "value" reference of a key, right?

George_George wrote:

why in current design of Dictionary, it is not allowed to add/remove elements

George_George wrote:

or change the value of key

George_George wrote:

...delete during foreach is not hard to implement and should not be expensive

private List<SomeType> myList = new List<SomeType>

// ...

// this is what supports foreach - it gets compiled into
// an IEnumerator class with MoveNext and Current methods
// (and i as a private field) by the compiler:
public System.Collections.Generic.IEnumerator<SomeType> GetEnumerator()
{
    for (int i = 0; i < myList.Length; i++)
    {
        yield return myList[i];
    }
}

// explicit implementation of non-generic version:
public System.Collections.Generic.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
    return this.GetEnumerator();
}

George_George wrote:

for example, why do we need to "copy a reference for each element into a temporary array when it is created"? Could you clarify or give more description please?

// my private list:
private List<SomeType> myList = new List<SomeType>
 
// other code...
 
// super-robust enumerator:
public System.Collections.Generic.IEnumerator<SomeType> GetEnumerator()
{
    SomeType[] elems = myList.ToArray(); // EXPENSIVE!
 
    for (int i = 0; i < elems.Length; i++)
    {
        yield return elems[i];
    }
}
 
// explicit implementation of non-generic version:
public System.Collections.Generic.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
    return this.GetEnumerator();
}

Guffa wrote:

Yes, assigning a reference is an atomic operation.

Assume var2 starts == 1.

Thread 1:
  var1 = var2;

Thread2:
  var2 = 2;
  var1 = 3;