Hands-On Design Patterns with Kotlin

Creating an email – first attempt

So, at 10 A.M., I plan to drink a coffee in my local cafe. But I also want to contact my manager, since my payslip didn't arrive yesterday. I attempt to create my first email like so:

val mail = Mail("[e-mail]", // TO    null,   // CC    null,   // BCC    "Ping", // Title    null    // Message)

This may have worked in Java, but in Kotlin this wouldn't compile, since we cannot pass null to List<String>. Null-safety is very important in Kotlin:

val mail = Mail("[e-mail]", // TO    listOf(),  // CC    listOf(),  // BCC    "Ping",    // Title    null       // Message) 

Note that since our constructor receives a lot of arguments, I had to put in some comments, so I wouldn't get lost.

The Kotlin compiler is smart enough to infer the ...