In ABAP, it is possible to use several types of parameters: importing, exporting, changing and returning. Here I list some reasons of why you should avoid using exporting parameters.
First, we have a method with an importing and returning parameter:
When we run the following unit test, it passes:
Now consider this example where we have a method with an exporting parameter:
This unit test fails:
This is a simple example, but it demonstrates the possible undesirable outcomes of using an exporting parameter, if it is misused (very common with less experienced programmers). Consider we had a more complicated scenario, this could lead to an inconsistent state (e.g. persisting the bar variable with an incorrect value).
So, as a rule of thumb, avoid exporting parameters. They are evil!
P.S.: Special thanks to Paulo Büttenbender and Michel Henrich for the peer review for this post.
¹ Martin, Robert C. Clean code: a handbook of agile software craftsmanship. Pearson Education, 2009. Pages 35 and 302
² Keller, Horst, and Wolf Hagen Thümmel. Official ABAP Programming Guidelines. Galileo Press, 2010. Page 293
1. You can have multiple exporting parameters
In a method, you can only have one returning parameter. By contrast, you can have multiple exporting parameters. This may lead to a method doing more than one thing, and as Robert Martin noted in his excellent book ‘Clean Code’, this is a code smell¹: "Functions should do one thing. They should do it well. They should do it only.".2. An exporting parameter is, behind the scenes, a changing parameter. This may lead to inconsistencies
Both changing and exporting parameters are passed by reference. Being so, inside the method they are directly handled with their real value, acting as pointer to the actual value. Their values are also modified even if the method leave early due to an exception². Consider the following examples:First, we have a method with an importing and returning parameter:
When we run the following unit test, it passes:
Now consider this example where we have a method with an exporting parameter:
This unit test fails:
This is a simple example, but it demonstrates the possible undesirable outcomes of using an exporting parameter, if it is misused (very common with less experienced programmers). Consider we had a more complicated scenario, this could lead to an inconsistent state (e.g. persisting the bar variable with an incorrect value).
3. Readability
Code should be easy to read, I find the importing/returning parameter syntax much cleaner:So, as a rule of thumb, avoid exporting parameters. They are evil!
P.S.: Special thanks to Paulo Büttenbender and Michel Henrich for the peer review for this post.
¹ Martin, Robert C. Clean code: a handbook of agile software craftsmanship. Pearson Education, 2009. Pages 35 and 302
² Keller, Horst, and Wolf Hagen Thümmel. Official ABAP Programming Guidelines. Galileo Press, 2010. Page 293
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