Why does this Kotlin method have enclosing backticks?

Question

What are the backticks used for in the snippet below?

Why add them around the fun is(amount:Int ):Boolean { ... }?

verifier.`is`(amount)

score 126 · Accepted Answer · edited Jun 20 '20 at 09:12

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 (`) character
foo.`is`(bar)

I'd also like to add that "in the wild", this is often used to have _identifier names with spaces_ in them, [example](https://stackoverflow.com/a/58955270/771032). — MrCC, Nov 24 '20 at 06:05

score 23 · Answer 2 · answered Jan 27 '21 at 16:16

Useful for tests

Backticks are very useful in tests for long function names:

@Test
fun `adding 3 and 4 should be equal to 7`() {
    assertEquals(calculator.add(3, 4), 7)
}

This makes the function names more readable. We can add spaces and other special characters in the function names. However, remember to use it only in tests, it's against the Kotlin coding conventions of the regular code.

score 12 · Answer 3 · answered May 24 '17 at 05:19

12

It allows you to call a Java method whose name is a Kotlin keyword. It won't work if you leave out the backticks.

answered May 24 '17 at 05:19

wero

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score 11 · Answer 4 · answered May 24 '17 at 05:23

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

score 2 · Answer 5 · edited Aug 28 '20 at 15:57

2

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

edited Aug 28 '20 at 15:57

Lorin Hochstein

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answered May 24 '17 at 05:21

gildor

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score 1 · Answer 6 · answered May 24 '17 at 05:22

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

https://kotlinlang.org/docs/reference/java-interop.html

Why does this Kotlin method have enclosing backticks?

6 Answers6

Escaping for Java identifiers that are keywords in Kotlin

Useful for tests

Linked

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