Merge pull request #26 from SciML/as/parameter-indexing-proxy

feat: add `ParameterIndexingProxy`

docs/src/api.md

@@ -36,6 +36,7 @@ parameter_values
 set_parameter!
 getp
 setp
+ParameterIndexingProxy
 ```
 
 ### State indexing

docs/src/complete_sii.md

@@ -262,6 +262,35 @@ function SymbolicIndexingInterface.set_state!(integrator::ExampleIntegrator, val
 end
 ```
 
+# The `ParameterIndexingProxy`
+
+[`ParameterIndexingProxy`](@ref) is a wrapper around another type which implements the
+interface and allows using [`getp`](@ref) and [`setp`](@ref) to get and set parameter 
+values. This allows for a cleaner interface for parameter indexing. Consider the
+following example for `ExampleIntegrator`:
+
+```julia
+function Base.getproperty(obj::ExampleIntegrator, sym::Symbol)
+  if sym === :ps
+    return ParameterIndexingProxy(obj)
+  else
+    return getfield(obj, sym)
+  end
+end
+```
+
+This enables the following API:
+
+```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)
+
+integrator.ps[:a] # 4.0
+getp(integrator, :a)(integrator) # functionally the same as above
+
+integrator.ps[:b] = 3.0
+setp(integrator, :b)(integrator, 3.0) # functionally the same as above
+```
+
 # Implementing the `SymbolicTypeTrait` for a type
 
 The `SymbolicTypeTrait` is used to identify values that can act as symbolic variables. It

src/SymbolicIndexingInterface.jl

@@ -20,4 +20,6 @@ export Timeseries,
     NotTimeseries, is_timeseries, state_values, set_state!, current_time, getu, setu
 include("state_indexing.jl")
 
+export ParameterIndexingProxy
+include("parameter_indexing_proxy.jl")
 end

src/parameter_indexing_proxy.jl

@@ -0,0 +1,19 @@
+"""
+    struct ParameterIndexingProxy
+
+This struct wraps any struct implementing the symbolic indexing interface. It allows
+`getindex` and `setindex!` operations to get/set parameter values. Requires that the
+wrapped type support [`getp`](@ref) and [`setp`](@ref) for getting and setting
+parameter values respectively.
+"""
+struct ParameterIndexingProxy{T}
+    wrapped::T
+end
+
+function Base.getindex(p::ParameterIndexingProxy, idx)
+    return getp(p.wrapped, idx)(p.wrapped)
+end
+
+function Base.setindex!(p::ParameterIndexingProxy, val, idx)
+    return setp(p.wrapped, idx)(p.wrapped, val)
+end

test/parameter_indexing_test.jl

@@ -16,8 +16,8 @@ for (i, sym) in [(1, :a), (2, :b), ([1, 2], [:a, :b]), ((1, 2), (:a, :b))]
     get = getp(sys, sym)
     set! = setp(sys, sym)
     true_value = i isa Tuple ? getindex.((p,), i) : p[i]
-    @test get(fi) == true_value
+    @test get(fi) == ParameterIndexingProxy(fi)[sym] == true_value
     set!(fi, 0.5 .* i)
-    @test get(fi) == 0.5 .* i
+    @test get(fi) == ParameterIndexingProxy(fi)[sym] == 0.5 .* i
     set!(fi, true_value)
 end