Would somebody please help me understand what is happening w

Question

Would somebody please help me understand what is happening with a function declaration like the following `fun foo String = bar ` What I understand is that function foo takes no parameters and has a return type of String What is odd to me coming from other languages where I have never seen this is that it is valid for there to be no body declaration but just an equal sign after the return type assigning the return value as a constant If you could would you please provide a use case for a function declared similarly

stephan_marshay · Answer

An example that comes to mind is for a concrete implementation of a method defined in an interface e g ``` interface MyInterface fun foo String class MyClass MyInterface override fun foo = bar ```

Casey Brooks · Answer

It s just syntax sugar It uses the right hand side of the `=` as the body of the function but can infer the return type of that function based on that expression

Casey Brooks · Answer

It s quite handy for implementing interfaces with static values as Stephen pointed out and also nice for wrapping functions without having to indent the whole thing For example making a test method work with coroutines becomes quite nice ``` Test fun test getResult is not suspending expectThat getResult isEqualTo some value Test fun testMySuspendingFunction = runBlocking lt Unit gt someone made getResult suspending No worries just add runBlocking to the test method signature for a clean diff expectThat getResult isEqualTo some value ```

Novoa · Answer

So it makes a little more sense now for sure I think the most confusing thing is that we re defining a return type but never using the return keyword If ` = ` is supposed to be the function body it d essentially be ``` fun foo String bar ``` Which doesn t make any sense because a return is never used and bar isn t assigned to anything This would throw an error in a language like java I guess by assigning the value to the return type I should just imagine that Kotlin just infers the return is the value assigned to the return type

stephan_marshay · Answer

no if you want to write it all out it would be ``` fun foo String return bar ```

Novoa · Answer

Thanks Stephan and Casey for the examples I appreciate the responses slightly smiling face

Casey Brooks · Answer

Think of the `=` more in the mathematical sense or in a functional programming sense It is not saying that `foo ` has or returns the value of the expression It is saying that `foo ` is equivalent to the expression and any call to that function can effectively be replaced by the expression

Novoa · Answer

Very well put Casey That s a great way to remember this