Passing a generic List<> in C#

Question

I am going brain dead on this; I have several List' defined, based on specific classes (c1, c2, c3...). I have a method that will process information on these lists. What I want to do is pass in the specific list, but have the method accept the generic list, and then via typeof determine what specific work to do. I know its possible, but I cant seem to get the syntax right on the method side. so, for example:

List<c1> c1var;
List<c2> c2var;
List<c3> c3var;

some_method(c1var);
some_method(c2var);
some_method(c3var);

class some_thing
some_method(List<> somevar)
if typeof(somevar).name = x then
esle if typeof(somevar).name = y then....

How do I set up the parameter list for the method?

thanks in advance R. Sanders

Quick question, why wouldn't you overload some_method to accept specific types of lists instead of doing typeof? — Brian H
– Brian H, Commented Jan 12, 2010 at 17:53

JSBձոգչ · Accepted Answer · 2010-01-12 17:47:32Z

55

You need to declare some_method to be generic, as well.

void SomeMethod<T>(List<T> someList)
{
    if (typeof(T) == typeof(c1))
    {
         // etc
    }
}

answered Jan 12, 2010 at 17:47

JSBձոգչ

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1 Comment

Brian H Over a year ago

Careful using typeof like that. That will check that the types are exactly the same without respecting the type hierarchy. As a result, something like MemoryStream and Stream will not evaluate to the same type (typeof(MemoryStream) == typeof(Stream) evaluates to false). This may be desired, but it's something to be aware of. Using the 'is' keyword is the typical way of evaluating types because "MemoryStream is Stream" will evaluate to true since they share the same object hierarchy.

Brian H · Accepted Answer · 2010-01-12 18:20:52Z

11

Careful with the use of typeof(typ1) == typeof(typ2). That will test to see if the types are equivalent disregarding the type hierarchy.

For example:

typeof(MemoryStream) == typeof(Stream); // evaluates to false
new MemoryStream() is Stream; //evalutes to true

A better way to check to see if an object is of a type is to use the 'is' keyword. An example is below:

public static void RunSnippet()
{
    List<c1> m1 = new List<c1>();
    List<c2> m2 = new List<c2>();
    List<c3> m3 = new List<c3>();

    MyMeth(m1);
    MyMeth(m2);
    MyMeth(m3);
}

public static void MyMeth<T>(List<T> a)
{
    if (a is List<c1>)
    {
        WL("c1");
    }
    else if (a is List<c2>)
    {
        WL("c2");
    }
    else if (a is List<c3>)
    {
        WL("c3");
    }
}

edited Jan 12, 2010 at 18:20

answered Jan 12, 2010 at 18:09

Brian H

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Comments

GxG · Accepted Answer · 2010-01-12 17:48:38Z

0

in the parameter section put List then try in the code switch(typeof(T){case typeof(int): break;})

answered Jan 12, 2010 at 17:48

GxG

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