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/estimator/global_metric.jl

@@ -29,9 +29,21 @@ function -(cost1::CDCost, cost2::CDCost)::CDCost
     return (data = d, computeEffort = ce, computeIntensity = ce / d)::CDCost
 end
 
+function isless(cost1::CDCost, cost2::CDCost)::Bool
+    return cost1.data + cost1.computeEffort < cost2.data + cost2.computeEffort
+end
+
+function zero(type::Type{CDCost})
+    return (data = 0.0, computeEffort = 00.0, computeIntensity = 0.0)::CDCost
+end
+
+function typemax(type::Type{CDCost})
+    return (data = Inf, computeEffort = Inf, computeIntensity = 0.0)::CDCost
+end
+
 struct GlobalMetricEstimator <: AbstractEstimator end
 
-function cost_type(estimator::GlobalMetricEstimator)
+function cost_type(estimator::GlobalMetricEstimator)::Type{CDCost}
     return CDCost
 end
 
@@ -51,15 +63,15 @@ end
 function operation_effect(estimator::GlobalMetricEstimator, graph::DAG, operation::NodeReduction)
     s = length(operation.input) - 1
     return (
-        data = s * -data(operation.input[1].task),
-        computeEffort = s * -compute_effort(operation.input[1].task),
+        data = s * -data(task(operation.input[1])),
+        computeEffort = s * -compute_effort(task(operation.input[1])),
         computeIntensity = typeof(operation.input) <: DataTaskNode ? 0.0 : Inf,
     )::CDCost
 end
 
 function operation_effect(estimator::GlobalMetricEstimator, graph::DAG, operation::NodeSplit)
-    s = length(operation.input.parents) - 1
-    d = s * data(operation.input.task)
-    ce = s * compute_effort(operation.input.task)
+    s::Float64 = length(parents(operation.input)) - 1
+    d::Float64 = s * data(task(operation.input))
+    ce::Float64 = s * compute_effort(task(operation.input))
     return (data = d, computeEffort = ce, computeIntensity = ce / d)::CDCost
 end

src/estimator/interface.jl

@@ -20,7 +20,7 @@ function cost_type end
 """
     graph_cost(estimator::AbstractEstimator, graph::DAG)
 
-Get the total estimated cost of the graph. The cost's data type can be chosen by the implementation, but should have usable comparison operators (<, <=, >, >=, ==) and basic math operators (+, -, *, /).
+Get the total estimated cost of the graph. The cost's data type can be chosen by the implementation, but must have a usable lessthan comparison operator (<), basic math operators (+, -) and an implementation of `zero()` and `typemax()`.
 """
 function graph_cost end