svcc2013-ImmutabilityHttpRequestBuilderDSL.scala

//Newman has a DSL for building up HttpRequests.
//the DSL uses the familiar builder pattern from Java.
//it copies the state of the request on each call, instead of modifying any internal state.

val url = new URL("http://siliconvalley-codecamp.com")

//the familiar GET function returns an instance of a Builder
//you can convert any Builder to a Newman HttpRequest
val builder1 = GET(url)

//we can add headers to any Builder.
//addHeaders copies the existing Builder to a new one with the headers
val builder2 = builder1.addHeaders("X-SVCC-Hello", "World")

//we can't add a body to a GET, so this won't compile.
//remember type safety?
val builder3 = builder1.addBody("Hello SVCC!")

//but we can add a body to a POST request, so this will compile
val builder4 = POST(url).addBody("Hello SVCC!")

//we can call toRequest on any Builder object to copy all its information into an HttpRequest
val req = builder4.toRequest
...

a few notes on performance:

• we debated the performance of this immutable system a few times over, because it does so many copies
• each object the DSL creates and subsequently copies is small and usually is short lived in most of our internal code
• because they're small, they're fast to copy
• because they're small and recycle fast, they go into the GC eden space and we usually don't pay a memory allocation penalty
• regardless this model is less performant than a mutable state model, but the tradeoff is highly reusable and threadsafe code