Kotlin Language Features Related to Null Handling

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Any software engineer with a Java background would find the null handling features in the Kotlin language interesting. Let's summarize this topic with some examples. Nullable types: In Kotlin, types are non-nullable by default. If you want a variable to be able to hold a null value, you need to explicitly declare its type as nullable using the Type? syntax. For example, String? denotes a nullable string, while String represents a non-nullable string. Safe calls (?.): Kotlin introduces the safe call operator (?.) for handling nullable types. It allows you to safely invoke a method or access a property on a nullable object. If the object is null, the expression returns null instead of throwing a NullPointerException. Example: data class Person(val name: String, val age: Int, val address: String?) fun main() {     // Create a person with a nullable address     val person1 = Person("John Doe", 25, "123 Main Street")     val person2 = Person("Jane Doe", 30,...
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Real life TestDrivenDevelopment benefit: Tests as Documentation

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I ve been working on an integration component that listens to LDAP server and notifies applications about changes on LDAP entries. My component searches for LDAP change logs. And a change log has the "targetdn" attribute.

Example:
targetDn:
uid=ND2392,ou=Users,dc=MyCompany

There is a business rule about notification process:
If Organization Unit is “Special Users”, skip the notification for that change.

Example:
targetDn:
uid=ND2392,ou=Special Users,dc=MyCompany
 
This changeLog should be skipped because it is about "Special Users" organization unit.

I am using a regular expression to parse the targetdn.
I isolated the code that does parsing and wrote unit tests for many inputs. Of course I added a unit test for the Business Rule mentioned above.

At a point, I thought my regular expression is not good enough and changed it:

Old regex:
[oO][uU]=[^,]*

New regex:
[oO][uU]=[^,\s]*

I was getting prepared to commit my code to Clearcase but I said:
“Just a minute! Lets run all unit tests first..”

After running all tests, I saw that 1 test failed. The test about the business rule failed!
That failure informed me that changing the regex was not a good idea. IT REMINDED ME ABOUT THE BUSINESS RULE. IT SERVED AS DOCUMENTATION.
I love this kind of documentation that not just sits there but helps :)

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