diff --git a/Project.toml b/Project.toml
index 46cbad5..88114a1 100644
--- a/Project.toml
+++ b/Project.toml
@@ -5,12 +5,14 @@ version = "0.3.1"
 
 [compat]
 Aqua = "0.8"
+SafeTestsets = "0.0.1"
 Test = "1"
 julia = "1.10"
 
 [extras]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
+SafeTestsets = "1bc83da4-3b8d-516f-aca4-4fe02f6d838f"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Aqua", "Test"]
+test = ["Aqua", "Test", "SafeTestsets"]
diff --git a/docs/src/api.md b/docs/src/api.md
index bc60cac..dc6a579 100644
--- a/docs/src/api.md
+++ b/docs/src/api.md
@@ -18,9 +18,13 @@ all_variable_symbols
 all_symbols
 solvedvariables
 allvariables
+state_values
 parameter_values
+current_time
 getp
 setp
+getu
+setu
 ```
 
 # Traits
diff --git a/docs/src/complete_sii.md b/docs/src/complete_sii.md
index e714718..035eec1 100644
--- a/docs/src/complete_sii.md
+++ b/docs/src/complete_sii.md
@@ -85,22 +85,41 @@ These are for handling symbolic expressions and generating equations which are n
 in the solution vector.
 
 ```julia
+using RuntimeGeneratedFunctions
+RuntimeGeneratedFunctions.init(@__MODULE__)
+
 # this type accepts `Expr` for observed expressions involving state/parameter/observed
 # variables
 SymbolicIndexingInterface.is_observed(sys::ExampleSystem, sym) = sym isa Expr || sym isa Symbol && haskey(sys.observed, sym)
 
 function SymbolicIndexingInterface.observed(sys::ExampleSystem, sym::Expr)
+  # generate a function with the appropriate signature
   if is_time_dependent(sys)
-    return function (u, p, t)
-      # compute value from `sym`, leveraging `variable_index` and
-      # `parameter_index` to turn symbols into indices
-    end
+    fn_expr = :(
+      function gen(u, p, t)
+        # assign a variable for each state symbol it's value in u
+        $([:($var = u[$idx]) for (var, idx) in pairs(sys.state_index)]...)
+        # assign a variable for each parameter symbol it's value in p
+        $([:($var = p[$idx]) for (var, idx) in pairs(sys.parameter_index)]...)
+        # assign a variable for the independent variable
+        $(sys.independent_variable) = t
+        # return the value of the expression
+        return $sym
+      end
+    )
   else
-    return function (u, p)
-      # compute value from `sym`, leveraging `variable_index` and
-      # `parameter_index` to turn symbols into indices
-    end
+    fn_expr = :(
+      function gen(u, p)
+        # assign a variable for each state symbol it's value in u
+        $([:($var = u[$idx]) for (var, idx) in pairs(sys.state_index)]...)
+        # assign a variable for each parameter symbol it's value in p
+        $([:($var = p[$idx]) for (var, idx) in pairs(sys.parameter_index)]...)
+        # return the value of the expression
+        return $sym
+      end
+    )
   end
+  return @RuntimeGeneratedFunction(fn_expr)
 end
 ```
 
@@ -127,7 +146,7 @@ only responsible for identifying observed values and `observed` will always be c
 on a type that wraps this type. An example is `ModelingToolkit.AbstractSystem`, which
 can identify whether a value is observed, but cannot implement `observed` itself.
 
-Other optional methods relate to parameter indexing. If a type contains the values of
+Other optional methods relate to indexing functions. If a type contains the values of
 parameter variables, it must implement [`parameter_values`](@ref). This allows the
 default definitions of [`getp`](@ref) and [`setp`](@ref) to work. While `setp` is
 not typically useful for solution objects, it may be useful for integrators. Typically,
@@ -140,7 +159,51 @@ function SymbolicIndexingInterface.parameter_values(sys::ExampleSystem)
 end
 ```
 
-## Implementing the `SymbolicTypeTrait` for a type
+If a type contains the value of state variables, it can define [`state_values`](@ref) to
+enable the usage of [`getu`](@ref) and [`setu`](@ref). These methods retturn getter/
+setter functions to access or update the value of a state variable (or a collection of
+them). If the type also supports generating [`observed`](@ref) functions, `getu` also
+enables returning functions to access the value of arbitrary expressions involving
+the system's symbols. This also requires that the type implement
+[`parameter_values`](@ref) and [`current_time`](@ref) (if the system is time-dependent).
+
+Consider the following `ExampleIntegrator`
+
+```julia
+mutable struct ExampleIntegrator
+  u::Vector{Float64}
+  p::Vector{Float64}
+  t::Float64
+  state_index::Dict{Symbol,Int}
+  parameter_index::Dict{Symbol,Int}
+  independent_variable::Symbol
+end
+```
+
+Assume that it implements the mandatory part of the interface as described above, and
+the following methods below:
+
+```julia
+SymbolicIndexingInterface.state_values(sys::ExampleIntegrator) = sys.u
+SymbolicIndexingInterface.parameter_values(sys::ExampleIntegrator) = sys.p
+SymbolicIndexingInterface.current_time(sys::ExampleIntegrator) = sys.t
+```
+
+Then the following example would work:
+```julia
+integrator = ExampleIntegrator([1.0, 2.0, 3.0], [4.0, 5.0], 6.0, Dict(:x => 1, :y => 2, :z => 3), Dict(:a => 1, :b => 2), :t)
+getx = getu(integrator, :x)
+getx(integrator) # 1.0
+
+get_expr = getu(integrator, :(x + y + t))
+get_expr(integrator) # 13.0
+
+setx! = setu(integrator, :y)
+setx!(integrator, 0.0)
+getx(integrator) # 0.0
+```
+
+# Implementing the `SymbolicTypeTrait` for a type
 
 The `SymbolicTypeTrait` is used to identify values that can act as symbolic variables. It
 has three variants:
diff --git a/src/SymbolicIndexingInterface.jl b/src/SymbolicIndexingInterface.jl
index 32b6f9e..1635737 100644
--- a/src/SymbolicIndexingInterface.jl
+++ b/src/SymbolicIndexingInterface.jl
@@ -15,4 +15,7 @@ include("symbol_cache.jl")
 export parameter_values, getp, setp
 include("parameter_indexing.jl")
 
+export state_values, current_time, getu, setu
+include("state_indexing.jl")
+
 end
diff --git a/src/state_indexing.jl b/src/state_indexing.jl
new file mode 100644
index 0000000..9ce95c3
--- /dev/null
+++ b/src/state_indexing.jl
@@ -0,0 +1,127 @@
+"""
+    state_values(p)
+
+Return an indexable collection containing the values of all states in the integrator or
+problem `p`.
+"""
+function state_values end
+
+"""
+    current_time(p)
+
+Return the current time in the integrator or problem `p`.
+"""
+function current_time end
+
+"""
+    getu(sys, sym)
+
+Return a function that takes an integrator or problem of `sys`, and returns the value of
+the symbolic `sym`. `sym` can be a direct index into the state vector, a symbolic state,
+a symbolic expression involving symbolic quantities in the system `sys`, or an
+array/tuple of the aforementioned.
+
+At minimum, this requires that the integrator or problem implement [`state_values`](@ref).
+To support symbolic expressions, the integrator or problem must implement
+[`observed`](@ref), [`parameter_values`](@ref) and [`current_time`](@ref).
+
+This function typically does not need to be implemented, and has a default implementation
+relying on the above functions.
+"""
+function getu(sys, sym)
+    symtype = symbolic_type(sym)
+    elsymtype = symbolic_type(eltype(sym))
+
+    if symtype != NotSymbolic()
+        _getu(sys, symtype, sym)
+    else
+        _getu(sys, elsymtype, sym)
+    end
+end
+
+function _getu(sys, ::NotSymbolic, sym)
+    return function getter(prob)
+        return state_values(prob)[sym] 
+    end
+end
+
+function _getu(sys, ::ScalarSymbolic, sym)
+    if is_variable(sys, sym)
+        idx = variable_index(sys, sym)
+        return function getter1(prob)
+            return state_values(prob)[idx]
+        end
+    elseif is_observed(sys, sym)
+        fn = observed(sys, sym)
+        if is_time_dependent(sys)
+            function getter2(prob)
+                return fn(state_values(prob), parameter_values(prob), current_time(prob))
+            end
+        else
+            function getter3(prob)
+                return fn(state_values(prob), parameter_values(prob))
+            end
+        end
+    end
+    error("Invalid symbol $sym for `getu`")
+end
+
+function _getu(sys, ::ScalarSymbolic, sym::Union{<:Tuple,<:AbstractArray})
+    getters = getu.((sys,), sym)
+    _call(getter, prob) = getter(prob)
+    return function getter(prob)
+        return _call.(getters, (prob,))
+    end
+end
+
+function _getu(sys, ::ArraySymbolic, sym)
+    return getu(sys, collect(sym))
+end
+
+"""
+    setu(sys, sym)
+
+Return a function that takes an integrator or problem of `sys` and a value, and sets the
+the state `sym` to that value. Note that `sym` can be a direct numerical index, a symbolic state, or an array/tuple of the aforementioned.
+
+Requires that the integrator implement [`state_values`](@ref) and the
+returned collection be a mutable reference to the state vector in the integrator/problem.
+In case `state_values` cannot return such a mutable reference, `setu` needs to be
+implemented manually.
+"""
+function setu(sys, sym)
+    symtype = symbolic_type(sym)
+    elsymtype = symbolic_type(eltype(sym))
+
+    if symtype != NotSymbolic()
+        _setu(sys, symtype, sym)
+    else
+        _setu(sys, elsymtype, sym)
+    end
+end
+
+function _setu(sys, ::NotSymbolic, sym)
+    return function setter!(prob, val)
+        state_values(prob)[sym] = val
+    end
+end
+
+function _setu(sys, ::ScalarSymbolic, sym)
+    is_variable(sys, sym) || error("Invalid symbol $sym for `setu`")
+    idx = variable_index(sys, sym)
+    return function setter!(prob, val)
+        state_values(prob)[idx] = val
+    end
+end
+
+function _setu(sys, ::ScalarSymbolic, sym::Union{<:Tuple,<:AbstractArray})
+    setters = setu.((sys,), sym)
+    _call!(setter!, prob, val) = setter!(prob, val)
+    return function setter!(prob, val)
+        _call!.(setters, (prob,), val)
+    end
+end
+
+function _setu(sys, ::ArraySymbolic, sym)
+    return setu(sys, collect(sym))
+end
diff --git a/src/trait.jl b/src/trait.jl
index 6660e91..4235114 100644
--- a/src/trait.jl
+++ b/src/trait.jl
@@ -35,13 +35,14 @@ struct NotSymbolic <: SymbolicTypeTrait end
     symbolic_type(::Type)
 
 Get the symbolic type trait of a type. Default to [`NotSymbolic`](@ref) for all types
-except `Symbol`.
+except `Symbol` and `Expr`, both of which are [`ScalarSymbolic`](@ref).
 
 See also: [`ScalarSymbolic`](@ref), [`ArraySymbolic`](@ref), [`NotSymbolic`](@ref)
 """
 symbolic_type(x) = symbolic_type(typeof(x))
 symbolic_type(::Type) = NotSymbolic()
 symbolic_type(::Type{Symbol}) = ScalarSymbolic()
+symbolic_type(::Type{Expr}) = ScalarSymbolic()
 
 """
     hasname(x)
diff --git a/test/example_test.jl b/test/example_test.jl
index 965d1b4..5d3caa0 100644
--- a/test/example_test.jl
+++ b/test/example_test.jl
@@ -1,3 +1,6 @@
+using SymbolicIndexingInterface
+using Test
+
 struct SystemMockup
     static::Bool
     vars::Vector{Symbol}
diff --git a/test/fallback_test.jl b/test/fallback_test.jl
index f390178..622d868 100644
--- a/test/fallback_test.jl
+++ b/test/fallback_test.jl
@@ -1,4 +1,5 @@
 using SymbolicIndexingInterface
+using Test
 
 struct Wrapper{W}
     wrapped::W
diff --git a/test/parameter_indexing_test.jl b/test/parameter_indexing_test.jl
index 66b1893..455dba7 100644
--- a/test/parameter_indexing_test.jl
+++ b/test/parameter_indexing_test.jl
@@ -1,6 +1,8 @@
 using SymbolicIndexingInterface
+using Test
 
-struct FakeIntegrator{P}
+struct FakeIntegrator{S,P}
+    sys::S
     p::P
 end
 
@@ -9,7 +11,7 @@ SymbolicIndexingInterface.parameter_values(fp::FakeIntegrator) = fp.p
 
 sys = SymbolCache([:x, :y, :z], [:a, :b], [:t])
 p = [1.0, 2.0]
-fi = FakeIntegrator(copy(p))
+fi = FakeIntegrator(sys, copy(p))
 for (i, sym) in [(1, :a), (2, :b), ([1, 2], [:a, :b]), ((1, 2), (:a, :b))]
     get = getp(sys, sym)
     set! = setp(sys, sym)
diff --git a/test/runtests.jl b/test/runtests.jl
index beeda77..5dbabc2 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,20 +1,25 @@
 using SymbolicIndexingInterface
+using SafeTestsets
 using Test
-@testset "Quality Assurance" begin
+
+@safetestset "Quality Assurance" begin
     @time include("qa.jl")
 end
-@testset "Interface test" begin
+@safetestset "Interface test" begin
     @time include("example_test.jl")
 end
-@testset "Trait test" begin
+@safetestset "Trait test" begin
     @time include("trait_test.jl")
 end
-@testset "SymbolCache test" begin
+@safetestset "SymbolCache test" begin
     @time include("symbol_cache_test.jl")
 end
-@testset "Fallback test" begin
+@safetestset "Fallback test" begin
     @time include("fallback_test.jl")
 end
-@testset "Parameter indexing test" begin
+@safetestset "Parameter indexing test" begin
     @time include("parameter_indexing_test.jl")
 end
+@safetestset "State indexing test" begin
+    @time include("state_indexing_test.jl")
+end
diff --git a/test/state_indexing_test.jl b/test/state_indexing_test.jl
new file mode 100644
index 0000000..87a1a8f
--- /dev/null
+++ b/test/state_indexing_test.jl
@@ -0,0 +1,22 @@
+using SymbolicIndexingInterface
+
+struct FakeIntegrator{S,U}
+    sys::S
+    u::U
+end
+
+SymbolicIndexingInterface.symbolic_container(fp::FakeIntegrator) = fp.sys
+SymbolicIndexingInterface.state_values(fp::FakeIntegrator) = fp.u
+
+sys = SymbolCache([:x, :y, :z], [:a, :b], [:t])
+u = [1.0, 2.0, 3.0]
+fi = FakeIntegrator(sys, copy(u))
+for (i, sym) in [(1, :x), (2, :y), (3, :z), ([1, 2], [:x, :y]), ((3, 2), (:z, :y))]
+    get = getu(sys, sym)
+    set! = setu(sys, sym)
+    true_value = i isa Tuple ? getindex.((u,), i) : u[i]
+    @test get(fi) == true_value
+    set!(fi, 0.5 .* i)
+    @test get(fi) == 0.5 .* i
+    set!(fi, true_value)
+end
diff --git a/test/symbol_cache_test.jl b/test/symbol_cache_test.jl
index 39e388d..5fb1b03 100644
--- a/test/symbol_cache_test.jl
+++ b/test/symbol_cache_test.jl
@@ -1,3 +1,6 @@
+using SymbolicIndexingInterface
+using Test
+
 sc = SymbolCache([:x, :y, :z], [:a, :b], [:t])
 
 @test all(is_variable.((sc,), [:x, :y, :z]))