c# - how do I create this particular generic method?

Question

I have a table (my own not DataTable) class witch holds a collection of

   KeyValuePairs<string,Type> [] columns ;

now the Type value assist's me in my app. for example when i need to create a "DB index" ( a B+tree )

I require the type of the field witch the key would be of ( of its type )

Now what I'm attempting to do is create a generic method which would return that index by acquiring the name of the field and the table from witch it is from.

The tree referencing the method does not know what type the field would be of my attempt was as follows :

the method :

 public BTree<T,object> CreateIndex<T>(string path,string FieldName) where T : IComparable

in main ( or where ever ) :

   Type index_type = table.Columns[2].Value;// the type
   string field = table.Columns[2].Key; // the name of the field
   BTree< 'type goes here',object> tree = CreateIndex<'type goes here'>(csv_path,field_name);

I wasn't able to find a way to extract the type ...

I thought putting it as it self index_type, object would do the trick i also tried casting the type threw

         Type.GetType(index_type.Name)
         Type.GetType(index_type.FullName)
         Type.GetType(index_type)
         Type.GetType(index_type.GetType())

          index_type.GetType() by itself

but cant seem to get it to except it as a type. if I of course give the type every thing works fine.

     BTree<float,object> tree = reader.CreateIndex<float>(csv, field);

You'll probably find this helpful [How to use reflection to call generic Method?](http://stackoverflow.com/questions/232535/how-to-use-reflection-to-call-generic-method) — Ken Wayne VanderLinde, Jul 06 '11 at 02:52
[csharpgeneral/thread](http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/fbacd5fd-829b-4db4-9bf8-5d1e0dab952b) shows how to use reflection to get the type for an almost identical question. — Justin Shield, Jul 06 '11 at 03:24

score 1 · Accepted Answer · answered Jul 06 '11 at 03:28

// the class that contains the CreateIndex<T> method.  Note that you will have to change the BindingFlags if this method is static

public class IndexCreator
{

    // your method
    public BTree<T, object> CreateIndex<T>(string path, string fieldName)
            where T : IComparable
    {
        // method body
    }

    // generic method
    public object CreateIndex(Type indexType, string path, string fieldName)
    {
        var genericMethod = GetType()
            .GetMethods(BindingFlags.Public | BindingFlags.Instance)
            .Single(methodInfo => methodInfo.Name == "CreateIndex" && methodInfo.IsGenericMethodDefinition)
            .MakeGenericMethod(indexType);
        return genericMethod.Invoke(this, new object[]{path, fieldName});

    }

}

score 0 · Answer 2 · answered Jul 06 '11 at 04:04

0

A bit shorter than smartcaveman would be

Activator.CreateInstance(typeof(BTree<>).MakeGenericType(indextype, typeof(object)), new object[]{arguments to constructor})

but it does require a class and a default constructor

answered Jul 06 '11 at 04:04

Cine

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c# - how do I create this particular generic method?

2 Answers2