CA1004: Generic methods should provide type parameter
| Item | Value |
|---|---|
| RuleId | CA1004 |
| Category | Microsoft.Design |
| Breaking change | Breaking |
Cause
The parameter signature of an externally visible generic method does not contain types that correspond to all the type parameters of the method.
Rule description
Inference is how the type argument of a generic method is determined by the type of argument that is passed to the method, instead of by the explicit specification of the type argument. To enable inference, the parameter signature of a generic method must include a parameter that is of the same type as the type parameter for the method. In this case, the type argument does not have to be specified. When you use inference for all type parameters, the syntax for calling generic and nongeneric instance methods is identical. This simplifies the usability of generic methods.
How to fix violations
To fix a violation of this rule, change the design so that the parameter signature contains the same type for each type parameter of the method.
When to suppress warnings
Do not suppress a warning from this rule. Providing generics in a syntax that is easy to understand and use reduces the time that is required to learn and increases the adoption rate of new libraries.
Example
The following example shows the syntax for calling two generic methods. The type argument for InferredTypeArgument is inferred, and the type argument for NotInferredTypeArgument must be explicitly specified.
Imports System
Namespace DesignLibrary
Public Class Inference
' This method violates the rule.
Sub NotInferredTypeArgument(Of T)()
Console.WriteLine(GetType(T))
End Sub
' This method satisfies the rule.
Sub InferredTypeArgument(Of T)(sameAsTypeParameter As T)
Console.WriteLine(sameAsTypeParameter)
End Sub
End Class
Class Test
Shared Sub Main()
Dim infer As New Inference()
infer.NotInferredTypeArgument(Of Integer)()
infer.InferredTypeArgument(3)
End Sub
End Class
End Namespace
using System;
namespace DesignLibrary
{
public class Inference
{
// This method violates the rule.
public void NotInferredTypeArgument<T>()
{
Console.WriteLine(typeof(T));
}
// This method satisfies the rule.
public void InferredTypeArgument<T>(T sameAsTypeParameter)
{
Console.WriteLine(sameAsTypeParameter);
}
}
class Test
{
static void Main()
{
Inference infer = new Inference();
infer.NotInferredTypeArgument<int>();
infer.InferredTypeArgument(3);
}
}
}
Related rules
CA1005: Avoid excessive parameters on generic types
CA1010: Collections should implement generic interface
CA1000: Do not declare static members on generic types
CA1002: Do not expose generic lists
CA1006: Do not nest generic types in member signatures
CA1003: Use generic event handler instances
CA1007: Use generics where appropriate