Cause

An externally visible generic type has more than two type parameters.

Rule description

The more type parameters a generic type contains, the more difficult it is to know and remember what each type parameter represents. It is usually obvious with one type parameter, as in List<T>, and in certain cases with two type parameters, as in Dictionary<TKey, TValue>. If more than two type parameters exist, the difficulty becomes too great for most users (for example, TooManyTypeParameters<T, K, V> in C# or TooManyTypeParameters(Of T, K, V) in Visual Basic).

How to fix violations

To fix a violation of this rule, change the design to use no more than two type parameters.

When to suppress warnings

Do not suppress a warning from this rule unless the design absolutely requires more than two type parameters. 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.

Types and methods should not have too many generic parameters

A method or class with too many type parameters has likely aggregated too many responsibilities and should be split.

Noncompliant Code Example

With the default parameter value of 2:

<S, T, U, V> void foo() {} // Noncompliant; not really readable
<String, Integer, Object, String>foo(); // especially on invocations