test StringBuilder

test.cs

int size = 100000;
long start;

List<string> list = new List<string>(size);

for(var i = 0; i < size; i++)
list.Add($"string_{i}");

Console.WriteLine("Aggregate string:");
start = DateTime.Now.Ticks;
list.Aggregate("", (a, b) => a + "," + b);
Console.WriteLine(new TimeSpan(DateTime.Now.Ticks - start));

Console.WriteLine("Join:");
start = DateTime.Now.Ticks;
string.Join(",", list);
Console.WriteLine(new TimeSpan(DateTime.Now.Ticks - start));

Console.WriteLine("Aggregate StringBuilder:");
start = DateTime.Now.Ticks;
list.Aggregate(new StringBuilder(""), (a, b) => a.Append(",").Append(b));
Console.WriteLine(new TimeSpan(DateTime.Now.Ticks - start));

Console.WriteLine("Aggregate $:");
start = DateTime.Now.Ticks;
list.Aggregate("", (a, b) => $"{a},{b}");
Console.WriteLine(new TimeSpan(DateTime.Now.Ticks - start));