Add parameters function (#5)

* Add 'parameters' function

* Add fallback

Author: eliascarv

src/interface.jl

@@ -61,6 +61,13 @@ object is valid for the `transform`.
 """
 function assertions end
 
+"""
+    parameters(transform)
+
+Returns a named tuple with the adjustable parameters of the `transform`.
+"""
+function parameters end
+
 """
     prep = preprocess(transform, object)
 
@@ -108,6 +115,8 @@ isinvertible(::Type{<:Transform}) = false
 
 assertions(transform::Transform) = []
 
+parameters(transform::Transform) = (;)
+
 preprocess(transform::Transform, object) = nothing
 
 reapply(transform::Transform, object, cache) = apply(transform, object) |> first

test/runtests.jl

@@ -17,6 +17,8 @@ using Test
   @test !TransformsBase.isrevertible(T → T)
   @test !TransformsBase.isinvertible(T → T)
   @test TransformsBase.assertions(T) |> isempty
+  @test TransformsBase.parameters(T) isa NamedTuple
+  @test TransformsBase.parameters(T) |> isempty
   @test TransformsBase.preprocess(T, nothing) |> isnothing
   @test TransformsBase.reapply(T, 1, nothing) == 1