fix: handle case when argument to cached function can be UInt

Author: AayushSabharwal

src/cache.jl

@@ -5,6 +5,17 @@ Sentinel value used for a cache miss, since cached functions may return `nothing
 """
 struct CacheSentinel end
 
+"""
+    $(TYPEDEF)
+
+Struct wrapping the `objectid` of a `BasicSymbolic`, since arguments annotated
+`::Union{BasicSymbolic, UInt}` would not be able to differentiate between looking
+up a symbolic or a `UInt`.
+"""
+struct SymbolicKey
+    id::UInt
+end
+
 """
     associated_cache(fn)
 
@@ -226,7 +237,7 @@ macro cache(args...)
         end
         if !Meta.isexpr(arg, :(::))
             # if the type is `Any`, branch on it being a `BasicSymbolic`
-            push!(keyexprs, :($arg isa BasicSymbolic ? objectid($arg) : $arg))
+            push!(keyexprs, :($arg isa BasicSymbolic ? $SymbolicKey(objectid($arg)) : $arg))
             push!(argexprs, arg)
             push!(keytypes, Any)
             continue
@@ -238,19 +249,17 @@ macro cache(args...)
         if Meta.isexpr(Texpr, :curly) && Texpr.args[1] == :Union
             Texprs = Texpr.args[2:end]
             Ts = map(Base.Fix1(Base.eval, __module__), Texprs)
-            keyTs = map(x -> x <: BasicSymbolic ? UInt64 : x, Ts)
-            if any(x -> x <: BasicSymbolic, Ts)
-            end
+            keyTs = map(x -> x <: BasicSymbolic ? SymbolicKey : x, Ts)
             push!(keytypes, Union{keyTs...})
-            push!(keyexprs, :($argname isa BasicSymbolic ? objectid($argname) : $argname))
+            push!(keyexprs, :($argname isa BasicSymbolic ? $SymbolicKey(objectid($argname)) : $argname))
             continue
         end
 
         # use `eval` to get the type because we need to know if it's a `BasicSymbolic`
         T = Base.eval(__module__, Texpr)
         if T <: BasicSymbolic
-            push!(keytypes, UInt64) 
-            push!(keyexprs, :(objectid($argname)))
+            push!(keytypes, SymbolicKey) 
+            push!(keyexprs, :($SymbolicKey(objectid($argname))))
         else
             push!(keytypes, T)
             push!(keyexprs, argname)