Storing Data

The most common way to store data on the Ergo blockchain is by placing it in the registers during box creation.

Another to store data is by using context variables at the time a box is spent. However, we will only discuss the former approach here.

An Ergo box consists of ten registers (R0..R9), out of which the first four (R0..R3) are reserved by the protocol. The remaining six registers (R4..R9) are free for storing data and are empty by default. An empty register cannot be sandwiched between full registers.

The following snippet shows how to use registers in your code:

{
   val r4 = SELF.R4[GroupElement]
   if (r4.isDefined) {
      val x = r4.get
      proveDlog(x) 
   } else {
      proveDlog(decodePoint(fromBase64("AlCGOtZKh66KL+g8GvGoQDy1P1PkhthRHa2KBIh+WyNS")))
   } 
}

The line SELF.R4[GroupElement] returns an Option[GroupElement] type. The semantics of the Option type is exactly the same as in Scala. If the Option is defined, i.e., SELF.R4 indeed contains a GroupElement type, then the first branch is executed, otherwise, the second branch is executed.