feat: add specialized observed for solutions of DDEProblems

Author: AayushSabharwal

src/solutions/ode_solutions.jl

@@ -354,6 +354,35 @@ function (sol::AbstractODESolution)(t::AbstractVector{<:Number}, ::Type{deriv},
     return DiffEqArray(u, t, p, sol; discretes)
 end
 
+struct DDESolutionHistoryWrapper{T}
+    sol::T
+end
+
+function (w::DDESolutionHistoryWrapper)(p, t; idxs = nothing)
+    w.sol(t; idxs)
+end
+function (w::DDESolutionHistoryWrapper)(out, p, t; idxs = nothing)
+    w.sol(out, t; idxs)
+end
+function (w::DDESolutionHistoryWrapper)(p, t, deriv::Type{Val{i}}; idxs = nothing) where {i}
+    w.sol(t, deriv; idxs)
+end
+function (w::DDESolutionHistoryWrapper)(
+        out, p, t, deriv::Type{Val{i}}; idxs = nothing) where {i}
+    w.sol(out, t, deriv; idxs)
+end
+
+function SymbolicIndexingInterface.observed(
+        sol::ODESolution{T, N, uType,
+            uType2, DType, tType, rateType, discType, P},
+        sym) where {T, N, uType, uType2, DType, tType, rateType, discType, P <: DDEProblem}
+    return let histfn = DDESolutionHistoryWrapper(sol),
+        rawfn = SymbolicIndexingInterface.observed(symbolic_container(sol), sym)
+
+        fn(u, p, t) = rawfn(u, histfn, p, t)
+    end
+end
+
 # public API, used by MTK
 """
     create_parameter_timeseries_collection(sys, ps, tspan)