Use getsym instead of an explicitly generated function and avoid writeback if nothing is returned

src/systems/callbacks.jl

@@ -970,6 +970,14 @@ end
     end)
 end
 
+@generated function _generated_readback(integ, getters::NamedTuple{NS1, <:Tuple}) where {NS1}
+    getter_exprs = []
+    for name in NS1
+        push!(getter_exprs, :($name = getters.$name(integ)))
+    end
+    return :((; $(getter_exprs...)))
+end
+
 function check_assignable(sys, sym)
     if symbolic_type(sym) == ScalarSymbolic()
         is_variable(sys, sym) || is_parameter(sys, sym)

src/systems/imperative_affect.jl

@@ -189,18 +189,13 @@ function compile_user_affect(affect::ImperativeAffect, cb, sys, dvs, ps; kwargs.
         else
             zeros(sz)
         end
-    obs_fun = build_explicit_observed_function(
-        sys, Symbolics.scalarize.(obs_exprs);
-        mkarray = (es, _) -> MakeTuple(es))
-    obs_sym_tuple = (obs_syms...,)
+    geto_funs = NamedTuple{(obs_syms...,)}((getsym.((sys,), obs_exprs)...,))
 
     # okay so now to generate the stuff to assign it back into the system
+    getm_funs = NamedTuple{(mod_syms...,)}((getsym.((sys,), mod_exprs)...,))
+
     mod_pairs = mod_exprs .=> mod_syms
     mod_names = (mod_syms...,)
-    mod_og_val_fun = build_explicit_observed_function(
-        sys, Symbolics.scalarize.(first.(mod_pairs));
-        mkarray = (es, _) -> MakeTuple(es))
-
     upd_funs = NamedTuple{mod_names}((setu.((sys,), first.(mod_pairs))...,))
 
     if has_index_cache(sys) && (ic = get_index_cache(sys)) !== nothing
@@ -212,12 +207,10 @@ function compile_user_affect(affect::ImperativeAffect, cb, sys, dvs, ps; kwargs.
     let user_affect = func(affect), ctx = context(affect)
         function (integ)
             # update the to-be-mutated values; this ensures that if you do a no-op then nothing happens
-            modvals = mod_og_val_fun(integ.u, integ.p, integ.t)
-            upd_component_array = NamedTuple{mod_names}(modvals)
+            upd_component_array = _generated_readback(integ, getm_funs)
 
             # update the observed values
-            obs_component_array = NamedTuple{obs_sym_tuple}(obs_fun(
-                integ.u, integ.p, integ.t))
+            obs_component_array = _generated_readback(integ, geto_funs)
 
             # let the user do their thing
             upd_vals = user_affect(upd_component_array, obs_component_array, ctx, integ)

test/symbolic_events.jl

@@ -1461,3 +1461,26 @@ end
     sys = structural_simplify(sys)
     sol = solve(ODEProblem(sys, [], (0.0, 1.0)), Tsit5())
 end
+
+@testset "Tuples in ImperativeAffect arguments" begin
+    @mtkmodel ImperativeAffectTupleMWE begin
+        @parameters begin
+            y(t) = 1.0
+        end
+        @variables begin
+            x(t) = 0.0
+        end
+        @equations begin
+            D(x) ~ y
+        end
+        @continuous_events begin
+            (x ~ 0.5) => ModelingToolkit.ImperativeAffect(
+                observed = (; mypars = (x, 2 * x)), modified = (; y)) do m, o, c, i
+                return (; y = 2 * o.mypars[1] + o.mypars[2])
+            end
+        end
+    end
+    @mtkbuild sys = ImperativeAffectTupleMWE()
+    prob = ODEProblem(sys, [], (0.0, 1.0))
+    sol = solve(prob, Tsit5())
+end