learning-kotlin | exercises allowing to learn Kotlin | Learning library

The following code is from https://github.com/gbaldeck/learning-kotlin/blob/master/src/main/kotlin/org/learning/DSLconstruction.kt

I find it hard to understand.

1: The fun buildString only accept one lambda parameter in Section A, why are there two parameters passed in Section B?

2: What is full code of Section B?
Such as

I am trying to learn Kotlin, and test how it works with spring boot. My application is using a mongo database to store data and I have a Jersey resource for retrieving data. I am testing it using spring-boot-test and RestTestTemplate.

The RestTestTemplate has an exchange method which takes a ParameterizedTypeReference. This class has a protected constructor. So the only way I managed to use it from Kotlin was like this:

class ListOfPeople : ParameterizedTypeReference>()

Here is my test-method: