Foreach with extension method for IEnumerable

Question

Quick question, see this code:

List<int> result = new List<int>();

var list = new List<int> { 1, 2, 3, 4 };

list.Select(value =>
    {
        result.Add(value);//Does not work??
        return value;
    });

AND:

result.Count == 0 //true

Why is result.Add (value) not executing?

However, this is not done. Another question that has a way to make foreach on IEnumerable with the Extention Method ?

Besides: IEnumerable.ToList().Foreach(p=>...)

Answer 1

Why is result.Add (value) not executing?

This is because LINQ uses delayed execution. Until you list the results (return Select), delegates will not be executed.

To demonstrate, try the following:

List<int> result = new List<int>();

var list = new List<int> { 1, 2, 3, 4 };

var results = list.Select(value =>
    {
        result.Add(value);//Does not work??
        return value;
    });

foreach(var item in results)
{
     // Just iterating through this will cause the above to execute...
}

, . LINQ , . Select , .

. , foreach IEnumerable ?

:

public static void ForEach<T>(this IEnumerable<T> items, Action<T> action)
{
    foreach(var item in items)
         action(item);
}

. . .

Answer 2

, , . , , , "ToArray" :

list.Select(value =>
    {
        result.Add(value);//Does not work??
        return value;
    }).ToArray();

Answer 3

List<int> result = new List<int>();
var list = new List<int> { 1, 2, 3, 4 };
list.ForEach(delegate(int sValue)
{
    result.Add(sValue);
});

, 1 2 3 4 . . .