Functions / methods in Scala. How does this work?

Question

I am new to Scala and have a hard time understanding all the ways of declaring and using functions. Can someone please explain, step by step, what is going on here?

I am

Answer 1

In your snippets there are several features of the Scala language and the compiler, let's analyse the ones I know:

def route = ...

defines a functions with no arguments and with result type determined by the return value of its body.

path("hello") {
  ...
}

I'm not familiar with the path function itself but it seems as if there are three things going on in that snippet:

• Currying: it's kinda "grouping arguments together";
• Curly braces instead of round braces: to give a different look-and-feel to the call;
• by-name parameters: to pass a code that will be evaluated only when needed.

I don't want to spend time describing all of them as internet is full of resources that explain them greatly. But I want to link at least this great introductory article that helped me a lot in my early days.

The linked article shows you a full example on how to use all three features to build your own control structure like the one of the code you're using.

Moving on, the bit

get {
  ...  
}

is again an application of the above points but this time there isn't currying so the curly braces are the only argument to the function.

complete("Hello, World!")

Is just a plain old function call.

In short that code uses some "tricks" that transform a function call into sometehing that resembles a special language construct and this can create confusion for the beginners.

This tecnique is used frequently to write Domani-Specific Languages (DSL) in Scala.

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