Support parameters in wire[] to override dependencies

[adamw]

(One of the ideas from ScalaDays 2014 - by @matthewfarwell)

The wire[] method could accept parameters, which would be used to wire an instance of the given type; the parameters would take precedence over (override) vals/defs in wider scopes.

Example usage:

class Service(s2: Service2, s3: Service3, config: Map[String, String])

lazy val s2 = wire[Service2]
lazy val s3 = wire[Service3]
lazy val defaultConfig = Map("username" -> "default")

// here the given map would be used instead of the default
lazy val sA = wire[Service](Map("username" -> "admin"))

// here the default config map would be used and an alternative Service2 impl
lazy val sB = wire[Service](new Service2(...))

A parameter which doesn't match any of the constructor parameters of the wired type would result in a compile-time error.

This can be useful for:

• providing alternative implementations only for a single usage
• providing configuration values on a per-instance basis

[ktoso]

+1
Make the error messages extra good on this one; could potentially be quite confusing sometimes (when ambiguous).

[ewiner]

As a workaround, you can kind of trick Macwire to do this by making a factory then using it just once:

lazy val sA = {
  def make(config: Map[String, String]): Service = wire[Service]
  make(Map("username" -> "admin"))
}

[adamw]

That must be the first MacWire hack - nice ;)

[backuitist]

Since #11 is implemented you can also do this:

lazy val sA = {
   val config = Map("username" -> "admin")
   wire[Service]
}

The advantage over wire[Service](Map("username" -> "admin")) is that you get to name your params.

[phkorn]

Since #11 is implemented you can also do this:

lazy val sA = {
   val config = Map("username" -> "admin")
   wire[Service]
}

The advantage over wire[Service](Map("username" -> "admin")) is that you get to name your params.

Can we add this method of solving ambiguity to the readme? In some cases it seems like a more practical approach than using Qualifiers

[adamw]

@k0rn1 please do, PR will be great :)