Question

Tried with :

IList<IList<string>> matrix = new List<new List<string>()>();

but I can’t. How can I do it? I need a matrix of strings…

Answer 1

You’d need:

IList<IList<string>> matrix = new List<IList<string>>();

but then you can happen to always add a List<string> for each element.

The reason this won’t work:

// Invalid
IList<IList<string>> matrix = new List<List<string>>();

is that it would then be reasonable to write:

// string[] implements IList<string>
matrix.Add(new string[10]);

… but that would violate the fact that the list is really a List<List<string>> – it’s got to contain List<string> values, not just any IList<string>… whereas my declaration at the top just creates a List<IList<string>>, so you could add a string array to it without breaking type safety.

Of course, you could change to use the concrete type in your declaration instead:

IList<List<string>> matrix = new List<List<string>>();

or even:

List<List<string>> matrix = new List<List<string>>();