Convert all T values using LINQ and assign them to an array of different type

Question

I wish to be able to modify some parameter value of generic type T, and I am trying to do this with LINQ, but I cannot figure it out.
Here is what I have:

public static T ConvertParam(T param)
{    
    T val = param.Select(i => { i = (T)ModifyValue(Convert.ToDouble(i)); });

    return val;
}

public static UInt64 ModifyValue(double value)
{
    UInt64 result = (UInt64)(value) * 3 + 1;

    return result;
}

In this case the problem resides in the value returned by "ModifyValue()" that needs to be cast to whatever T param contains, but I am not sure how to do that. T can be an int, uint, int[], uint[], etc.
Handling the arrays is also tricky.

I have also tried with a normal for loop as here below:

public static T ConvertParam(T param)
{
    List<UInt64> output = new List<UInt64>();

    foreach (var v in param)
    {
        output.Add(ModifyValue(Convert.ToDouble(v));
    }

    return output.ToArray();
}

The problem here again is that the returned value may or may not be an array. It should just return the modified version of T param.

EDIT

Note that ModifyValue() is just a dummy example. "param" MUST be generic!

EDIT 2

Maybe I could do something around these lines (not sure how to though):

public static T ConvertParam(T param)
{
    T ret = param.ToList().ConvertAll(i => i = new T() { ModifyValue(Convert.ToDouble(i)) });

    return ret;
}

ConvertParam should have generic type argument T, otherwise ist declaration is invalid — Pavel Anikhouski
– Pavel Anikhouski, Commented May 28, 2020 at 8:17
So based on what the ModifyValue is doing, is your value always a double? — devcrp
– devcrp, Commented May 28, 2020 at 8:26
How do you intend on calling ConvertParam? Why do you think it should be generic? — Sweeper
– Sweeper, Commented May 28, 2020 at 8:26
Why are you converting input to double only to cast it to UInt64 ? — Guru Stron
– Guru Stron, Commented May 28, 2020 at 8:26
@stackMeUp if your value is always a double why do you need generics? — Marco Salerno
– Marco Salerno, Commented May 28, 2020 at 8:33

Mike Hanson · Accepted Answer · 2020-05-28 09:02:28Z

1

It doesn't look to me like that would actually compile.

I think you have two vital things missing first as Pavel suggested in his comment you are returning T from ConvertParam and it takes and argument of T, but you haven't declared T.

Secondly, you are using LINQ against a generic type, but there is nothinh that allows the compiler to know that param is queryable by LINQ. I think you need to change your code to something like this


public static IEnumerable<T> ConvertParam<T>(IEnumerable<T> param)
{
    // This seems redundant
    // List<UInt64> output = new List<UInt64>(); 

    var val = param.Select(i => (T)ModifyValue(Convert.ToDouble(i)));

    return val;
}

public static UInt64 ModifyValue(double value)
{
    UInt64 result = (UInt64)(value) * 3 + 1;

    return result;
}

EDIT: As others have said I'm not sure your code makes sense from a use case point of view.

edited May 28, 2020 at 9:02

answered May 28, 2020 at 8:28

Mike Hanson

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3 Comments

Stejin Over a year ago

I was about to write more or less the same. ;)

stackMeUp Over a year ago

Thanks, that does work either. Maybe my use of "Select" is incorrect?

Mike Hanson Over a year ago

Just noticed your Select is indeed incorrect, you are assigning something new to i but not returning it. Have updated answer

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