What are the backticks used for in the snippet below?
Why add them around the fun is(amount:Int ):Boolean { ... }?
verifier.`is`(amount)
It's because is is a reserved keyword in Kotlin. Since Kotlin is supposed to be interoperable with Java and is is a valid method (identifier) name in Java, the backticks are used to escape the method so that it can be used as a method without confusing it as a keyword. Without it it will not work because it would be invalid syntax.
This is highlighted in the Kotlin documentation:
Escaping for Java identifiers that are keywords in Kotlin
Some of the Kotlin keywords are valid identifiers in Java:
in,object,is, etc. If a Java library uses a Kotlin keyword for a method, you can still call the method escaping it with the backtick (`) characterfoo.`is`(bar)
It allows you to call a Java method whose name is a Kotlin keyword. It won't work if you leave out the backticks.
The backtick are a "workaround" to allow you to call methods that have a name representing a Kotlin keyword.
See kotlinlang:
Some of the Kotlin keywords are valid identifiers in Java: in, object, is, etc. If a Java library uses a Kotlin keyword for a method, you can still call the method escaping it with the backtick (`) character
is in list of Kotlin reserved words
To use Kotlin reserved word (such as is or object) for function/class name you should wrap it to backticks
Some of the Kotlin keywords are valid identifiers in Java: in, object, is, etc. If a Java library uses a Kotlin keyword for a method, you can still call the method escaping it with the backtick (`) character
来源：https://stackoverflow.com/questions/44149474/why-does-this-kotlin-method-have-enclosing-backticks