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Convert a collection of items to a string

Sunt cazuri cand avem liste pe care dorim sa le convertim intr-un string folosind un anumit delimitator.
List<string> lista=new List<string>(){ "A" , "B" , "C" };
//Output: A, B, C,
LINQ nu contine o solutie directa, putem incerca sa interam cu un foreach toate elementele din lista si sa le adaugam la un StringBuilder
StringBuilder sb=new StringBuilder();
string format = "{0}, ";
lista.ForEach(item => sb.AppendFormat(format, item));
Dar din pacate codul scris mai sus este echivalent cu un foreach clasic, doar ca iteram folosind LINQ. O solutie este sa folosim metoda String.Join, care primeste doi parametrii:
-delimitatorul;
-un array care contine lista de string-uri;
Aceasta metoda functioneaza fara probleme, singura problema care o are este ca nu functioneaza pe obiecte generice de tip IEnumerable. Pentru a rezolva acest neajuns este sa apelam la extension method si sa ne scriem propria noastra metoda pentru IEnumerable.
 /// <summary>
/// For generic IEnumerable.
/// </summary>
/// <typeparam name="T">The generic type of IEnumerable.</typeparam>
/// <param name="source">The IEnumerable object.</param>
/// <param name="separator">The string separator.</param>
/// <returns>The string formed from the of each item of list.</returns>
public static string ToString<T>(this IEnumerable<T> source, string separator)
{
if (separator == null)
{
throw new ArgumentNullException("Parameter separator can not be null.");
}

return string.Join(
separator,
source
.Where(item => item != null)
.Select(item => item.ToString())
.ToArray());
}

/// <summary>
/// For generic IEnumerable.
/// </summary>
/// <param name="source">The IEnumerable object.</param>
/// <param name="separator">The string separator.</param>
/// <returns>The string formed from the of each item of list.</returns>
public static string ToString(this IEnumerable source, string separator)
{
if (separator == null)
{
throw new ArgumentNullException("Parameter separator can not be null.");
}

string[] array = source.Cast<object>().Where(n => n != null).Select(n => n.ToString()).ToArray();

return string.Join(
separator,
source
.Cast<object>()
.Where(item => item != null)
.Select(item => item.ToString())
.ToArray());
}

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