Using Generics

In the .NET Framework, you can use generics to customize a method, class, structure, interface, field, or property according to the data type that it acts upon. Instead of writing a method, class, structure, interface, field, or property for a particular type, you can write it to use any type. When a generic is declared, the type is specified. For example, in C#, if you use the generic type parameter T, then you can write a List<T> class that is declared as either List<int>, List<string>, or List<MyClass>.

With .NET Framework interoperability, you can define DotNet variables for generics. You cannot specify generic type names in C/AL. When a generic is instantiated by a constructor in C/AL, all type names are set to the System.Object type. For example, if you have a mylist DotNet variable for the System.List<T> generic, you create an instance of mylist in C/AL as shown. mylist is instantiated as a List<Object> type.

mylist := mylist.List();

If a method returns an instance of a generic whose type name is defined, then the type name is applied. In the following C/AL example, the method returns a List<String> instance, and mylist is instantiated as a List<String> type.

mylist := x.GetAStringList();

Example

The following C/AL example constructs a string list, fills the list with data, and then uses the Item method to validate whether the list contains the expected data. The Item method is equivalent to a C# index operator.

Variable name	Data Type	SubType	Length
varDotNet	DotNet	'mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.System.Collections.Generic.List`1
textResult	Text		30
i	Integer
capacity	Integer

capacity := 5;
varDotNet := varDotNet.List(capacity);
FOR i:= 0 TO (capacity-1) DO
  varDotNet.Add(FORMAT(i));
IF varDotNet.Count <> capacity THEN
  ERROR('Wrong list count, expected {0}, actual {1}', capacity, 
    varDotNet.Count);
FOR i:= 0 TO (capacity-1) DO
BEGIN
  textResult := varDotNet.Item(i);
  IF textResult <> FORMAT(i) THEN
    ERROR('List index [%1] contains the wrong data, expected %2, actual
      %3', i, FORMAT(i), textResult);
END;