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3.4 Let - In  expressions

Let - In expressions serve for assigning a complex VOCL expression to a variable which can be used then. This expression is divided into two parts: on the left hand side (the Let part) you define the expression that should be assigned to a variable and on the right hand side (the In part) you can define arbitrary VOCL expression in which the variable can be used.
The expression on left side must have a ClassifierRole / SetClassifierRole which has the same rolename and roletype as the Constraint context, so that a translation to a OCL-String can be done.

3.4.1 Creating Let - In expressions

The creation of these expressions is done in few steps:

1. Select the entry Let-In-Expression in the editor palette.
2. Move the cursor inside a Constraint and click the left mouse button.
3. A dialog (see Fig. 3.4.1) is opened in which you have to specify a variable name, variable type and the alignment of the figure (vertical / horizontal).
   

Fig 3.4.1 - Let - In expression dialog

In Fig. 3.4.2 you can see the result in the editor. You see a figure which is divided into the Let and In part as mentioned above. In the left top corner the variable name and the variable type appear.

Fig. 3.4.2 - Simple Let - In expression


In Fig. 3.4.3 you can see a more complex example for Let - In expressions: On the left side there is a ClassifierRole with a method call getProfit() whose result is stored in the variable profit which belongs to the Let - In expression. Then, this variable is used on the right side in the if-then-else expression.

Fig. 3.4.3 - Complex Let - In expression example


Fig. 3.4.4 - Corresponding OCL-String of the previous example