interfaces in nim

interface.nim

# Interface
type InterfaceType = ref object of RootObj
  baseVar: int # optional var

# Virtual method of `InterfaceType`
method doSomething(this: InterfaceType) =
  discard # empty method

# Implementation
type ImplementType = ref object of InterfaceType
  someVar: int
  someVar2: int

# Implementation of virtual method `doSomething`
method doSomething(this: ImplementType) =
  this.someVar = 5
  this.baseVar = 5

  echo "two numbers: ", this.someVar, " ", this.baseVar


# Test
var impl = ImplementType()

impl.doSomething
# result: two numbers: 5 5


# Convert to base type
var base = InterfaceType(impl)

base.doSomething
# result: two numbers: 5 5