Optimizer interface and sample implementation (#19)

Reviewed-on: Rubydragon/MetagraphOptimization.jl#19
Co-authored-by: Anton Reinhard <anton.reinhard@proton.me>
Co-committed-by: Anton Reinhard <anton.reinhard@proton.me>

src/operation/iterate.jl

@@ -0,0 +1,39 @@
+import Base.iterate
+
+const _POSSIBLE_OPERATIONS_FIELDS = fieldnames(PossibleOperations)
+
+_POIteratorStateType =
+    NamedTuple{(:result, :state), Tuple{Union{NodeFusion, NodeReduction, NodeSplit}, Tuple{Symbol, Int64}}}
+
+@inline function iterate(possibleOperations::PossibleOperations)::Union{Nothing, _POIteratorStateType}
+    for fieldname in _POSSIBLE_OPERATIONS_FIELDS
+        iterator = iterate(getfield(possibleOperations, fieldname))
+        if (!isnothing(iterator))
+            return (result = iterator[1], state = (fieldname, iterator[2]))
+        end
+    end
+
+    return nothing
+end
+
+@inline function iterate(possibleOperations::PossibleOperations, state)::Union{Nothing, _POIteratorStateType}
+    newStateSym = state[1]
+    newStateIt = iterate(getfield(possibleOperations, newStateSym), state[2])
+    if !isnothing(newStateIt)
+        return (result = newStateIt[1], state = (newStateSym, newStateIt[2]))
+    end
+
+    # cycle to next field
+    index = findfirst(x -> x == newStateSym, _POSSIBLE_OPERATIONS_FIELDS) + 1
+
+    while index <= length(_POSSIBLE_OPERATIONS_FIELDS)
+        newStateSym = _POSSIBLE_OPERATIONS_FIELDS[index]
+        newStateIt = iterate(getfield(possibleOperations, newStateSym))
+        if !isnothing(newStateIt)
+            return (result = newStateIt[1], state = (newStateSym, newStateIt[2]))
+        end
+        index += 1
+    end
+
+    return nothing
+end