MethodBuilder.DefineGenericParameters(String[]) Method

Definition

Namespace:

System.Reflection.Emit

Assemblies:

netstandard.dll, System.Reflection.Emit.dll

Source:

MethodBuilder.cs

Sets the number of generic type parameters for the current method, specifies their names, and returns an array of GenericTypeParameterBuilder objects that can be used to define their constraints.

C#

public System.Reflection.Emit.GenericTypeParameterBuilder[] DefineGenericParameters(params string[] names);

Parameters

names

String[]

An array of strings that represent the names of the generic type parameters.

Returns

GenericTypeParameterBuilder[]

An array of GenericTypeParameterBuilder objects representing the type parameters of the generic method.

Exceptions

InvalidOperationException

Generic type parameters have already been defined for this method.

-or-

The method has been completed already.

-or-

The SetImplementationFlags(MethodImplAttributes) method has been called for the current method.

ArgumentNullException

names is null.

-or-

An element of names is null.

ArgumentException

names is an empty array.

Examples

The following code example creates a dynamic type, DemoType, which contains the dynamic generic method DemoMethod. This method has two generic type parameters, one of which is used as a parameter, and the other as the return type.

When the code is executed, the dynamic assembly is saved as DemoGenericMethod1.dll, and can be examined using the Ildasm.exe (IL Disassembler).

Note

This code example generates a simple method body that merely returns a null reference. For a code example with a more fully developed method body that creates and uses generic types, see How to: Define a Generic Method with Reflection Emit.

C#

using System;
using System.Reflection;
using System.Reflection.Emit;

class DemoMethodBuilder
{

    public static void Main()
    {
        // Creating a dynamic assembly requires an AssemblyName
        // object, and the current application domain.
        //
        AssemblyName asmName =
            new AssemblyName("DemoMethodBuilder1");
        AppDomain domain = AppDomain.CurrentDomain;
        AssemblyBuilder demoAssembly =
            domain.DefineDynamicAssembly(
                asmName,
                AssemblyBuilderAccess.RunAndSave
            );

        // Define the module that contains the code. For an
        // assembly with one module, the module name is the
        // assembly name plus a file extension.
        ModuleBuilder demoModule =
            demoAssembly.DefineDynamicModule(
                asmName.Name,
                asmName.Name + ".dll"
            );

        TypeBuilder demoType = demoModule.DefineType(
            "DemoType",
            TypeAttributes.Public | TypeAttributes.Abstract
        );

        // Define a Shared, Public method with standard calling
        // conventions. Do not specify the parameter types or the
        // return type, because type parameters will be used for
        // those types, and the type parameters have not been
        // defined yet.
        MethodBuilder demoMethod = demoType.DefineMethod(
            "DemoMethod",
            MethodAttributes.Public | MethodAttributes.Static
        );

        // Defining generic parameters for the method makes it a
        // generic method. By convention, type parameters are
        // single alphabetic characters. T and U are used here.
        //
        string[] typeParamNames = {"T", "U"};
        GenericTypeParameterBuilder[] typeParameters =
            demoMethod.DefineGenericParameters(typeParamNames);

        // The second type parameter is constrained to be a
        // reference type.
        typeParameters[1].SetGenericParameterAttributes(
            GenericParameterAttributes.ReferenceTypeConstraint);

        // Use the IsGenericMethod property to find out if a
        // dynamic method is generic, and IsGenericMethodDefinition
        // to find out if it defines a generic method.
        Console.WriteLine("Is DemoMethod generic? {0}",
            demoMethod.IsGenericMethod);
        Console.WriteLine("Is DemoMethod a generic method definition? {0}",
            demoMethod.IsGenericMethodDefinition);

        // Set parameter types for the method. The method takes
        // one parameter, and its type is specified by the first
        // type parameter, T.
        Type[] parms = {typeParameters[0]};
        demoMethod.SetParameters(parms);

        // Set the return type for the method. The return type is
        // specified by the second type parameter, U.
        demoMethod.SetReturnType(typeParameters[1]);

        // Generate a code body for the method. The method doesn't
        // do anything except return null.
        //
        ILGenerator ilgen = demoMethod.GetILGenerator();
        ilgen.Emit(OpCodes.Ldnull);
        ilgen.Emit(OpCodes.Ret);

        // Complete the type.
        Type dt = demoType.CreateType();

        // To bind types to a dynamic generic method, you must
        // first call the GetMethod method on the completed type.
        // You can then define an array of types, and bind them
        // to the method.
        MethodInfo m = dt.GetMethod("DemoMethod");
        Type[] typeArgs = {typeof(string), typeof(DemoMethodBuilder)};
        MethodInfo bound = m.MakeGenericMethod(typeArgs);
        // Display a string representing the bound method.
        Console.WriteLine(bound);

        // Save the assembly, so it can be examined with Ildasm.exe.
        demoAssembly.Save(asmName.Name + ".dll");
    }
}

/* This code example produces the following output:
Is DemoMethod generic? True
Is DemoMethod a generic method definition? True
DemoMethodBuilder DemoMethod[String,DemoMethodBuilder](System.String)
*/

Remarks

Calling the DefineGenericParameters method makes the current method generic. There is no way to undo this change. Calling this method a second time causes an InvalidOperationException.

The type parameters of the generic method can be retrieved later by using the GetGenericArguments method.

By convention, a type parameter name is a single uppercase letter.

For more information, see MethodBase.IsGenericMethod and MethodInfo.GetGenericMethodDefinition. For information on generic types, see Type.IsGenericType.

Applies to

See also

• MethodInfo
• IsGenericType
• DefineMethod
• How to: Define a Generic Method with Reflection Emit