fix: handle cases for calling oop setter directly on state/parameter object

src/state_indexing.jl

@@ -407,19 +407,27 @@ end
 FullSetter(ssetter, psetter) = FullSetter(ssetter, psetter, nothing, nothing)
 
 function (fs::FullSetter)(valp, val)
+    check_both_state_and_parameter_provider(valp)
+
     return fs.state_setter(valp, val[fs.state_split]),
     fs.param_setter(valp, val[fs.param_split])
 end
 
 function (fs::FullSetter{Nothing})(valp, val)
+    check_both_state_and_parameter_provider(valp)
+
     return state_values(valp), fs.param_setter(valp, val)
 end
 
 function (fs::(FullSetter{S, Nothing} where {S}))(valp, val)
+    check_both_state_and_parameter_provider(valp)
+
     return fs.state_setter(valp, val), parameter_values(valp)
 end
 
 function (fs::(FullSetter{Nothing, Nothing}))(valp, val)
+    check_both_state_and_parameter_provider(valp)
+
     return state_values(valp), parameter_values(valp)
 end
 

src/value_provider_interface.jl

@@ -238,12 +238,20 @@ struct OOPSetter{I, D}
 end
 
 function (os::OOPSetter)(valp, val)
-    buffer = os.is_state ? state_values(valp) : parameter_values(valp)
+    buffer = if os.is_state
+        hasmethod(state_values, Tuple{typeof(valp)}) ? state_values(valp) : valp
+    else
+        hasmethod(parameter_values, Tuple{typeof(valp)}) ? parameter_values(valp) : valp
+    end
     return remake_buffer(os.indp, buffer, (os.idxs,), (val,))
 end
 
 function (os::OOPSetter)(valp, val::Union{Tuple, AbstractArray})
-    buffer = os.is_state ? state_values(valp) : parameter_values(valp)
+    buffer = if os.is_state
+        hasmethod(state_values, Tuple{typeof(valp)}) ? state_values(valp) : valp
+    else
+        hasmethod(parameter_values, Tuple{typeof(valp)}) ? parameter_values(valp) : valp
+    end
     if os.idxs isa Union{Tuple, AbstractArray}
         return remake_buffer(os.indp, buffer, os.idxs, val)
     else
@@ -338,3 +346,20 @@ function Base.showerror(io::IO, err::NotVariableOrParameter)
       or `is_parameter`. Got `$(err.sym)` which is neither.
   """)
 end
+
+function MustBeBothStateAndParameterProviderError(missing_state::Bool)
+    ArgumentError("""
+        A setter returned from `setsym_oop` must be called with a value provider that \
+        contains both states and parameters. The given value provided does not \
+        implement `$(missing_state ? "state_values" : "parameter_values")`.
+        """)
+end
+
+function check_both_state_and_parameter_provider(valp)
+    if !hasmethod(state_values, Tuple{typeof(valp)}) || state_values(valp) === valp
+        throw(MustBeBothStateAndParameterProviderError(true))
+    end
+    if !hasmethod(parameter_values, Tuple{typeof(valp)}) || parameter_values(valp) === valp
+        throw(MustBeBothStateAndParameterProviderError(false))
+    end
+end

test/parameter_indexing_test.jl

@@ -179,6 +179,8 @@ for sys in [
             newp = setter(fi, val)
             getter = getp(sys, sym)
             @test getter(newp) == val
+            newp = setter(parameter_values(fi), val)
+            @test getter(newp) == val
         end
     end
 end

test/state_indexing_test.jl

@@ -90,6 +90,8 @@ for (sym, val, newval, check_inference) in [(:x, u[1], 4.0, true)
     svals, pvals = setter(fi, newval)
     @test svals ≈ new_states
     @test pvals == parameter_values(fi)
+    @test_throws ArgumentError setter(state_values(fi), newval)
+    @test_throws ArgumentError setter(parameter_values(fi), newval)
 end
 
 for (sym, val, check_inference) in [
@@ -147,6 +149,8 @@ for (sym, oldval, newval, check_inference) in [(:a, p[1], 4.0, true)
     uvals, pvals = oop_setter(fi, newval)
     @test uvals ≈ newu
     @test pvals ≈ newp
+    @test_throws ArgumentError oop_setter(state_values(fi), newval)
+    @test_throws ArgumentError oop_setter(parameter_values(fi), newval)
 end
 
 for (sym, val, check_inference) in [