Generic function unable to compare between an array value and a standard value

Question

Essentially, I'm trying to write a generic bruteforce getMax() method for a matrix. Here is what I have:

 private T getMax <T>(T[,] matrix, uint rows, uint cols) where T : IComparable<T>
    {
        T max_val = matrix[0, 0];
        for (int row = 0; row < rows; ++row)
        {
            for (int col = 0; col < cols; ++col)
            {
                if (matrix[row, col] > max_val)
                {
                    max_val = matrix[row, col];
                }
            }
        }
        return max_val;
    }

This won't compile, with the error Operator '>' cannot be applied to operands of type 'T' and 'T'. I gave the IComparable directive, so I'm not sure what's going on here. Why does this not work?

Rather than passing the rows and columns to the method you can just use `GetLength` to find the dimensions, unless you specifically want to search a subset of the matrix. — Servy, Feb 26 '13 at 18:21

score 7 · Accepted Answer · answered Feb 26 '13 at 18:16

7

You must use CompareTo() rather than the > operation.

See here: http://msdn.microsoft.com/en-gb/library/system.icomparable.aspx

In your case you'd put:

if (matrix[row, col].CompareTo(max_val) > 0)

answered Feb 26 '13 at 18:16

Matthew Watson

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score 2 · Answer 2 · answered Feb 26 '13 at 18:18

2

Implementing IComparable means that it defines the CompareTo method, not that the > operator is defined. You need to use:

if (matrix[row, col].CompareTo(max_val) > 0) {

answered Feb 26 '13 at 18:18

tvanfosson

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score 1 · Answer 3 · answered Feb 26 '13 at 18:18

1

if (matrix[row, col] > max_val)

Should be

if (matrix[row, col].CompareTo(max_val) > 0)

Since IComparable provides only CompareTo not >.

answered Feb 26 '13 at 18:18

Guvante

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Generic function unable to compare between an array value and a standard value

3 Answers3