How to do a generic call to function based on a Type object?

Question

how do you execute Get, when all you have is: T expressed as a Type object i.e.

Type type=typeof(int);

and arguments param1 and param2?

    public void DoCall(){
        var type=typeof(int);
        // object o=Get<type> ("p1","p2");   //<-- wont work (expected)
        // *** what should go here? ***
    }

    public IEnumerable<T> Get<T>(string param1,string param2) {
        throw new NotImplementedException();
    }

This sort of generic method is for type safety at compile time. If you dont know the type at compile time there is a good chance you're using generics wrong, or should have an additional overload which takes the type as a parameter such as `public IEnumerable Get(Type type, string param1, string param2)`. — Jamiec, Sep 22 '11 at 13:35
@Jamiec: thanks for the comment Jamiec. I'll keep that in mind. One reason to keep is that I want to use whenever possible. I'd have to abandone usage for this case, or adopt two method signatures (one with , the other with Get(Type typ, ...) — sgtz, Sep 22 '11 at 13:42
@sgtz - having 2 methods is the *usual* way to deal with both possibilities. Its how most DA libraries handle this scenario. — Jamiec, Sep 22 '11 at 13:44

dtb · Accepted Answer · 2011-09-22T13:52:45.417

4

You need to use reflection:

public IEnumerable GetBoxed(Type type, string param1, string param2)
{
    return (IEnumerable)this
        .GetType()
        .GetMethod("Get")
        .MakeGenericMethod(type)
        .Invoke(this, new[] { param1, param2 });
}

edited Sep 22 '11 at 13:52

answered Sep 22 '11 at 13:33

dtb

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score 2 · Answer 2 · edited May 23 '17 at 11:55

2

MakeGenericMethod is the key:

var get = typeof(WhereverYourGetMethodIs).GetMethod("Get");
var genericGet = get.MakeGenericMethod(type);

edited May 23 '17 at 11:55

Community

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1

answered Sep 22 '11 at 13:32

Anton Gogolev

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+1 That looks close. Should we also provide args to "MakeGenericMethod"? – sgtz Sep 22 '11 at 13:37

score 0 · Answer 3 · answered Sep 22 '11 at 13:33

0

What's wrong with just using the generic type parameter directly?

public void DoCall(){
    IEnumerable<int> integers = Get<int> ("p1","p2");
    // ...
}

answered Sep 22 '11 at 13:33

Matt Ball

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score 0 · Answer 4 · answered Sep 22 '11 at 13:33

In the example above the 'T' will be whatever you pass into the Get method and it will also return the same IEnumerable. So if you do the following:

 IEnumerable<int> o = Get<int>("p1", "p2");

o will be IEnumerable

but if you want something else, then you just pass in a different Type, hence Generic types.

score 0 · Answer 5 · answered Sep 22 '11 at 13:35

If possible, you should redefine your Get method to take the type of object as an argument:

public IEnumerable<object> Get(object type, string param1,string param2)
{
}

Then if you really need it, you can rewrite the original generic method as follows:

public IEnumerable<T> Get<T>(string param1,string param2)
{
    var result = Get(typeof(T), param1, param2);
    return result.Cast<T>();
}

How to do a generic call to function based on a Type object?

5 Answers5