[RESOLVED] [2.0] Generics Without Generics Syntax

[penagate]

All,


I know that a class's constructor is callable via a hidden New method.

Is there a way of constructing a generic object using this type of hidden method?
I don't have access to a reflector right now, so I can't examine all the built-in methods.

(This is a general .NET question, not really a C# one. I'm not using C#, which is why I can't use the ClassName<type> syntax.)


Something along the lines of:

obj = List.NewGeneric('System.String')

—would be great.


Cheers,

— P

[jmcilhinney]

I'm not 100% sure what you mean. Are you saying that you want to, for example, create a new List<String> by specifying the generic type as a string at run time rather than as a type at design time?

[jmcilhinney]

If you answered "yes" to the previous question then try this:

// Create the general generic type.
Type baseType = typeof(List<>);
 
// Create the generic argument type.
Type argumentType = Type.GetType("System.String");
 
// Create the specific generic type.
Type derivedType = baseType.MakeGenericType(argumentType);
 
// Invoke the default constructor of the specific generic type to create an instance.
Object list = derivedType.InvokeMember(string.Empty,
                                       System.Reflection.BindingFlags.CreateInstance,
                                       null,
                                       null,
                                       null);
 
// Confirm the type of the object created.
MessageBox.Show(list.GetType().ToString());

[penagate]

That's almost, but not quite, what I meant.
Sorry, I typed the question in a rush to leave work.

I'm actually using APL. This has no native support for generics, so it has no generic syntax — but it is loosely typed, so it can support any .NET object once it is instantiated.

My problem is instantiating the object.
I can instantiate non-generic types by using the hidden New method, e.g.:

X ← ArrayList.New

I have no idea how to do that for a generic type, which is why I was looking for some other static method that might be present in the MSIL but not exposed in the Visual Studio IDE.


It isn't essential that I use generics, but it would be nice, since I hate using late-bound collections when generics are available.


(Your sample is interesting. I will try it, but can't quite at the moment guess how to convert the 'typeof' line.)


Thanks for the reply.

— P

[jmcilhinney]

This is a wild guess but maybe:

X ← List`1[String]

[penagate]

J,

On line two of your snippet you use typeof(List<>).

Is there a string equivalent for the List<> part, similar to how you've done it on line 5?

[jmcilhinney]

It would be "List`1", i.e. the List class with one generic type parameter. Note that that's not a single quote. It's the one on the same key as the tilde.

[penagate]

Perfect. Thanks.

[jmcilhinney]

Just did a quick test and, in C# at least, the class name has to be fully qualified in the string:

// Create the general generic type.
Type baseType = Type.GetType("System.Collections.Generic.List`1");