How can I initialize a IList<IList<string>>?

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...

Solution 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>>();

Solution 2

try this

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

Solution 3

This will work - you can't initialize a generic type parameter the way you tried:

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

Though, the inner IList<string> will be null. To initialize it you can do the following:

matrix.Add(new List<string>());

Solution 4

if matrix is of constant size arrays are a better fit

string[][] matrix = new string[size];
matrix[0] = new string[5];
matrix[1] = new string[8];
matrix[2] = new string[7];

and if it is rectangular

string[,] matrix = new string[sizex,sizey];

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