System.Linq.Expressions.Expression.Add methods

This article provides supplementary remarks to the reference documentation for this API.

The Add method returns a BinaryExpression that has the Method property set to the implementing method. The Type property is set to the type of the node. If the node is lifted, the IsLifted and IsLiftedToNull properties are both true. Otherwise, they are false. The Conversion property is null.

The following information describes the implementing method, the node type, and whether a node is lifted.

Implementing method

The following rules determine the selected implementing method for the operation:

• If the Type property of either left or right represents a user-defined type that overloads the addition operator, the MethodInfo that represents that method is the implementing method.
• Otherwise, if left.Type and right.Type are numeric types, the implementing method is null.

Node type and lifted versus non-lifted

If the implementing method is not null:

• If left.Type and right.Type are assignable to the corresponding argument types of the implementing method, the node is not lifted. The type of the node is the return type of the implementing method.

• If the following two conditions are satisfied, the node is lifted and the type of the node is the nullable type that corresponds to the return type of the implementing method:

  • left.Type and right.Type are both value types of which at least one is nullable and the corresponding non-nullable types are equal to the corresponding argument types of the implementing method.
  • The return type of the implementing method is a non-nullable value type.

If the implementing method is null:

• If left.Type and right.Type are both non-nullable, the node is not lifted. The type of the node is the result type of the predefined addition operator.
• If left.Type and right.Type are both nullable, the node is lifted. The type of the node is the nullable type that corresponds to the result type of the predefined addition operator.