Generics and the arithmetic problem C#

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hello everyone the following code is my attempt to create a generic class in C#
the idea is to create an Array of elements of the same type
the problem i ran into is when try trying to calculate the sum of the element in an array , generic classes in c# doesn't allow me to do arithmetics
any help please

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Devoire
{
    class Tableau<T>
    {
        private T[] tab;
        int cnt;

        public Tableau(int ss = 0)
        {
            tab = new T[ss];
            cnt = 0;
        }
        public Tableau(T[] ar, int count)
        {
            if (count > ar.Length)
                count = ar.Length;
            tab = new T[count];
            for (int i = 0; i < count; i++)
            {
                if (ar[i] != null)
                {
                    tab[i] = ar[i];
                    cnt++;
                }
            }
            
        }

        public T this[int index]
        {
            get {
                if( index < cnt)
                {
                    return tab[index];
                }
                else
                {
                    return default(T);
                }
            }
            set
            {

                    if (index >= cnt)
                    {
                        index = cnt++;
                    }
                    if (cnt > tab.Length)
                    {
                        T[] newtab = new T[cnt];
                        Array.Copy(tab, newtab, index);
                        tab = newtab;
                    }

                    tab[index] = value;

            }
        }
        public  static Tableau<T>   fusionner(Tableau<T> tabl, Tableau<T> tab2)
        {
            Tableau<T> tmp = new Tableau<T>(tabl.cnt + tab2.cnt);
            for(int i = 0 ; i < tabl.cnt ; i++)
            {
                tmp[i] = tabl[i];
            }
            for (int i = tabl.cnt , j = 0 ; i < tmp.taille; i++)
            {
                tmp[i] = tab2[j++];
            }
            return tmp;
            
        }
        public int taille
        {
            get
            {
                return tab.Length;
            }
        }
        public T Premier
        {
            get
            {
                return tab[0];
            }
            set
            {
                tab[0] = value;
                if (cnt == 0)
                    cnt++;
                             
            }
        }
        public override string ToString()
        {
            string s = "" ;
            for (int i = 0 ;  i < cnt ; i++)
            {

                s += tab[i] + " ";
            }
            return s;
        }
        public  Tableau<T> copie(Tableau<T> tabl)
        {
            cnt = tabl.cnt;
            tab = new T[cnt];
            for (int i = 0; i <cnt; i++ )
            {
                tab[i] = tabl[i];
            }
            return this;
        }

    }
    class Program
    {
        static void Main(string[] args)
        {
           
            double[] ar = { 1.2, 125.3, 3.3, 4, 10.3, 11, 12 };
            int[] ar1 = { 1, 125, 3, 4, 10, 11, 12 };
            int a = ar.Length;
            Tableau<double> tb = new Tableau<double>(ar,3);
            Tableau<int> tb2 = new Tableau<int>(ar1, 4);

            Tableau<int> tb3 = new Tableau<int>(15);
            tb3.Premier = 6;
            tb3.Premier = tb3.Premier *  (int)tb.Premier;
            Console.WriteLine(tb3);
        }
    }
}

What I have tried:

i search for a solution online but i didn't understand most of them
any help would great
thank you

Posted 30-May-16 8:12am

Member 12223678

Updated 30-May-16 12:02pm

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Comments

Philippe Mori 30-May-16 17:43pm

Generics are quite limited in .NET (compared to say templates in C++).

One could use some tricks like those proposed in solutions but for code like this (matrix operations), you might have an undesirable impact on performance (or the code might be too complex).

Thus, in the end, there is no easy way to do that and hard way might not be adequate anyway for problem like this one.

In a case like this, one would probably only write the double version in C# and possibly some conversion function from/to narrower types.

3 solutions

Solution 3

Indeed, as it is explained in Solution 2, is an interesting problem. Unfortunately, it does not have a perfect solution.
Please see my past answer:
Generics in C#: compile-time error, '+' cannot be applied[^],
Generic constraints on methods[^].

See also my comment to Solution 2.

—SA

Posted 30-May-16 12:02pm

Sergey Alexandrovich Kryukov

Updated 30-May-16 12:09pm

v3

Solution 1

Generics can't do arithmetic because not all classes support all the operations required. For example, while you can subtract two DateTime values to get a Timespan, what on earth would you get by adding them together? :laugh:
Because not all possible classes that could be the "target" of the generic support the operators, you can't use them on any generic type without explicitly casting them.
The exception is when you use a constraint on the type of the generic:

C#

private class myClass<T> where T : baseClass
    {

But...you can't use any constraint in this case, as int, double and so forth are structs, not classes and as such are implicitly sealed - a type constraint must be a derivable class.

Sorry - but you can't do what you want via generics!

Posted 30-May-16 8:27am

OriginalGriff

Comments

Member 12223678 30-May-16 14:31pm

thank you @OriginalGriff
maybe Microsoft will come up with a solution in the future

OriginalGriff 30-May-16 14:38pm

No, probably not.
It's not a "solvable" problem: it's a prerequisite of the way C# (and the whole of .NET) works. If the base class doesn't support an operation then it's derived classes don't have to either. And if it let you through now (because you "know" that all the classes you are going to use with the Generic do support add, subtract, multiply, and divide) then in a months time what happens when you use the class as part of an assembly, and pass it a DateTime? Your app crashes at runtime for an error that should have been caught at compile time!
As a result, the safe way to do it is to prevent your code compiling unless all applicable classes have to implement every method you are going to use on them.
Very, very unlikely to change!

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Henrik Jonsson · Accepted Answer · 2016-05-30T10:07:00

Interesting question.

Since not all types support arithmetics and there is no generic operator support in .NET you must inject a type-specific operator into your generic Tableau class.

To add support for addition you can add a delegate variable to your generic class like this

C#

public static Func<t,t,t> Addition;

which you then can invoke from a Sum function like this

C#

public T Sum()
{
    T sum = default(T);
    for (int i = 0; i < cnt; i++)
    {
       sum = Addition(sum, tab[i]);
    }
    return sum;
}

Before using this method you must "teach" the class how to add the types you want to use by simply assigning the Addition function once

C#

Tableau<int>.Addition = (a,b) => a+b;
Tableau<string>.Addition = (a,b) => a+b;</string></int>

for each type that you want to use.

I think this idea can be generalized (and improved by some encapsulation). If anyone finds it useful I may present in an article here.