diff --git a/bok-macro/src/collection.rs b/bok-macro/src/collection.rs
index bf3e14e..b393e89 100644
--- a/bok-macro/src/collection.rs
+++ b/bok-macro/src/collection.rs
@@ -60,6 +60,7 @@ pub(crate) fn collection(
         *
         #(#[::bok_macro::collection_dep(#all_deps_builder)])
         *
+        #[derive(::core::fmt::Debug)]
         pub struct Collection {
             repo: ::std::sync::Arc<#name>,
             pkgs: ::std::sync::RwLock<
diff --git a/bok-macro/src/pkgs.rs b/bok-macro/src/pkgs.rs
index 99e9e8c..b47a13f 100644
--- a/bok-macro/src/pkgs.rs
+++ b/bok-macro/src/pkgs.rs
@@ -58,7 +58,7 @@ pub(crate) fn package(attrs: TokenStream, input: TokenStream) -> TokenStream {
             || path.segments[1].ident.to_string() != "PkgEmpty"
         {
             let repo_argument = {
-                let generic_id: ::syn::Path = ::syn::parse_quote!(id<R>);
+                let generic_id: ::syn::Path = ::syn::parse_quote!(id<R, C>);
                 generic_id.segments.last().unwrap().arguments.clone()
             };
             path.segments.last_mut().unwrap().arguments = repo_argument;
@@ -103,7 +103,11 @@ pub(crate) fn package_path(
         .into();
     };
     let generic_struct: ::syn::ItemStruct = ::syn::parse_quote! {
-        pub struct test<R> where R: ::bok::Repository + 'static {}
+        pub struct test<R, C>
+        where
+            R: ::bok::Repository + 'static,
+            C: ::bok::Collection,
+        {}
     };
     let (_, generics, where_clause) = generic_struct.generics.split_for_impl();
 
@@ -142,9 +146,15 @@ pub(crate) fn package_path(
                     _bok_repo: ::std::marker::PhantomData<R>
                 })
                 .unwrap();
+            let collection_marker = ::syn::Field::parse_named
+                .parse2(quote! {
+                    _bok_collection: ::std::marker::PhantomData<C>
+                })
+                .unwrap();
             base_fields_extra.push(pkg_version);
             base_fields_extra.push(base_marker);
             base_fields_extra.push(repo_marker);
+            base_fields_extra.push(collection_marker);
         }
         None => {
             return ::syn::Error::new(
@@ -165,6 +175,7 @@ pub(crate) fn package_path(
         if id.to_string() == "version"
             || id.to_string() == "_bok_base"
             || id.to_string() == "_bok_repo"
+            || id.to_string() == "_bok_collection"
         {
             continue;
         }
@@ -359,8 +370,16 @@ pub(crate) fn package_impl(
             "BokDeps{}",
             t_id.path.segments.last().unwrap().ident
         );
+        let trait_deps_builder = ::quote::format_ident!(
+            "BokBuilderDeps{}",
+            t_id.path.segments.last().unwrap().ident
+        );
         let g: ::syn::ItemImpl = ::syn::parse_quote! {
-            impl<R> trait_name for #t_id<R> where R: ::bok::Repository + #trait_deps {}
+            impl<R, C> trait_name for #t_id<R, C>
+            where
+                R: #trait_deps,
+                C: #trait_deps_builder,
+            {}
         };
         ast.generics = g.generics;
         ast.self_ty = g.self_ty;
@@ -638,16 +657,30 @@ pub(crate) fn package_impl_builder(
                     };
                     Ok(actual_repo)
                 }?;
-                /*
                 let #arg_build = {
                     let build_any = #arg_build.0.as_any();
                     let Some(actual_build) =
-                        build_any.downcast_ref::<#trait_deps_builder>() else {
+                        build_any.downcast_ref::<C>() else {
                         return Err(());
                     };
-                    Ok(::bok::deps::Build(actual_build))
+                    Ok(actual_build)
+                }?;
+                let #arg_runtime = {
+                    let runtime_any = #arg_runtime.0.as_any();
+                    let Some(actual_runtime) =
+                        runtime_any.downcast_ref::<C>() else {
+                        return Err(());
+                    };
+                    Ok(actual_runtime)
+                }?;
+                let #arg_test = {
+                    let test_any = #arg_test.0.as_any();
+                    let Some(actual_test) =
+                        test_any.downcast_ref::<C>() else {
+                        return Err(());
+                    };
+                    Ok(actual_test)
                 }?;
-                */
                 Ok(())
             }
         };
@@ -675,6 +708,7 @@ pub(crate) fn package_impl_builder(
             if id.to_string() == "version"
                 || id.to_string() == "_bok_base"
                 || id.to_string() == "_bok_repo"
+                || id.to_string() == "_bok_collection"
             {
                 return None;
             }
@@ -705,6 +739,7 @@ pub(crate) fn package_impl_builder(
             if id.to_string() == "version"
                 || id.to_string() == "_bok_base"
                 || id.to_string() == "_bok_repo"
+                || id.to_string() == "_bok_collection"
             {
                 return None;
             }
@@ -735,6 +770,7 @@ pub(crate) fn package_impl_builder(
             if id.to_string() == "version"
                 || id.to_string() == "_bok_base"
                 || id.to_string() == "_bok_repo"
+                || id.to_string() == "_bok_collection"
             {
                 return None;
             }
@@ -765,6 +801,7 @@ pub(crate) fn package_impl_builder(
             if id.to_string() == "version"
                 || id.to_string() == "_bok_base"
                 || id.to_string() == "_bok_repo"
+                || id.to_string() == "_bok_collection"
             {
                 return None;
             }
@@ -822,30 +859,33 @@ pub(crate) fn package_impl_builder(
 
     quote! {
         #[derive(::std::default::Default, ::std::fmt::Debug)]
-        pub struct #name_builder<R>
+        pub struct #name_builder<R, C>
         where
-            R: ::bok::Repository + 'static + #trait_deps,
+            R: 'static + #trait_deps,
+            C: 'static + #trait_deps_builder
         {
             _bok_repo: ::std::marker::PhantomData<R>,
+            _bok_collection: ::std::marker::PhantomData<C>,
             #(#non_opt_fields: ::std::option::Option<#non_opt_types>,)*
             #(#opt_fields: ::std::option::Option<#opt_types>,)*
         }
         #[::macro_magic::export_tokens(#full_export_path_name)]
-        impl<R> ::bok::PkgBuilder for #name_builder<R>
+        impl<R, C> ::bok::PkgBuilder for #name_builder<R, C>
         where
-            R: ::bok::Repository + 'static + #trait_deps,
+            R: 'static + #trait_deps,
+            C: 'static + #trait_deps_builder,
         {
             fn name(&self) -> ::bok::PkgName {
                 use ::bok::Pkg;
-                #pkg_name::<R>::default().name()
+                #pkg_name::<R,C>::default().name()
             }
             fn path(&self) -> ::bok::Path<::bok::PkgName> {
                 use ::bok::Pkg;
-                #pkg_name::<R>::default().path()
+                #pkg_name::<R,C>::default().path()
             }
             fn version(&self) -> ::bok::Version {
                 use ::bok::Pkg;
-                #pkg_name::<R>::default().version()
+                #pkg_name::<R,C>::default().version()
             }
             fn as_any(&self) -> &dyn ::std::any::Any {
                 self
@@ -854,7 +894,7 @@ pub(crate) fn package_impl_builder(
                 self
             }
             fn default_unused(&mut self) -> &mut dyn ::bok::PkgBuilder {
-                let def = #pkg_name::<R>::default();
+                let def = #pkg_name::<R,C>::default();
                 #(if self.#non_opt_fields5.is_none() {
                     self.#non_opt_fields5 = Some(def.#non_opt_fields5);
                 })*
@@ -869,7 +909,7 @@ pub(crate) fn package_impl_builder(
                 #(if self.#non_opt_fields2.is_none() {
                     return ::std::result::Result::Err("unset field".into());
                 })*
-                let mut pkg = ::std::boxed::Box::new(#pkg_name::<R>::default());
+                let mut pkg = ::std::boxed::Box::new(#pkg_name::<R,C>::default());
                 #(pkg.#non_opt_fields3 = self.#non_opt_fields3.clone().unwrap();)
                 *
                 #(pkg.#opt_fields2 = self.#opt_fields2.clone();)
@@ -879,13 +919,16 @@ pub(crate) fn package_impl_builder(
             #(#local_funcs)
             *
         }
-        impl<R> #name_builder<R>
+        impl<R, C> #name_builder<R, C>
         where
-            R: ::bok::Repository +'static + #trait_deps,
+            R: 'static + #trait_deps,
+            C: 'static + #trait_deps_builder,
         {
+            // FIXME: difference from `::default()`?
             pub fn new() -> Self {
                 Self {
                     _bok_repo: ::std::marker::PhantomData::default(),
+                    _bok_collection: ::std::marker::PhantomData::default(),
                     #(#non_opt_fields6: None,)*
                     #(#opt_fields4: None,)*
                 }
@@ -937,9 +980,10 @@ pub(crate) fn package_impl_builder(
                 -> ::std::result::Result<(),()>;)
             *
         }
-        impl<R> #trait_options for #name_builder<R>
+        impl<R, C> #trait_options for #name_builder<R, C>
         where
-            R: ::bok::Repository +'static + #trait_deps,
+            R: 'static + #trait_deps,
+            C: 'static + #trait_deps_builder,
         {
             #(fn #non_opt_fields8 (&mut self, val : #non_opt_types4)
                 -> ::std::result::Result<(),()> {
@@ -1044,10 +1088,13 @@ pub(crate) fn package_impl_base_add(
     }
 
     let trait_deps = ::quote::format_ident!("BokDeps{}", name_pkg);
+    let trait_deps_builder =
+        ::quote::format_ident!("BokBuilderDeps{}", name_pkg);
     let generic_struct: ::syn::ItemImpl = ::syn::parse_quote! {
-        impl<R> test for #name_pkg <R>
+        impl<R, C> test for #name_pkg<R, C>
         where
-            R: ::bok::Repository + 'static + #trait_deps,
+            R: 'static + #trait_deps,
+            C: 'static + #trait_deps_builder,
         {}
     };
 
@@ -1156,21 +1203,24 @@ pub(crate) fn derive_package(input: TokenStream) -> TokenStream {
     }
 
     let trait_deps = ::quote::format_ident!("BokDeps{}", name);
+    let trait_deps_builder = ::quote::format_ident!("BokBuilderDeps{}", name);
 
     let expanded = quote! {
-        impl<R> ::core::fmt::Display for #name<R>
+        impl<R, C> ::core::fmt::Display for #name<R, C>
         where
-            R: ::bok::Repository + #trait_deps,
+            R: #trait_deps,
+            C: #trait_deps_builder,
         {
             fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>)
                 ->::core::fmt::Result
             {
-                <#name<R> as ::bok::PkgCode>::fmt(self, f)
+                <#name<R, C> as ::bok::PkgCode>::fmt(self, f)
             }
         }
-        impl<R> ::bok::PkgCode for #name<R>
+        impl<R, C> ::bok::PkgCode for #name<R, C>
         where
-            R: ::bok::Repository + 'static + #trait_deps,
+            R: 'static + #trait_deps,
+            C: 'static + #trait_deps_builder,
         {
             fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>)
                 ->::core::fmt::Result
@@ -1231,9 +1281,10 @@ pub(crate) fn derive_package(input: TokenStream) -> TokenStream {
                 f.write_str(&formatted)
             }
         }
-        impl<R> #name<R>
+        impl<R, C> #name<R, C>
         where
-            R: ::bok::Repository + 'static + #trait_deps + ::core::default::Default,
+            R: 'static + #trait_deps + ::core::default::Default,
+            C: 'static + #trait_deps_builder,
         {
             pub fn as_any(&self) -> &dyn ::std::any::Any {
                 self
diff --git a/bok-macro/src/repos.rs b/bok-macro/src/repos.rs
index f158e4a..d9c7942 100644
--- a/bok-macro/src/repos.rs
+++ b/bok-macro/src/repos.rs
@@ -279,7 +279,7 @@ pub(crate) fn repo_packages(
     //   "#[repo_packages(my::pkg)]" -->> "#[repo_packages(my::pkg<Self>)])"
     let mut rewrite = false;
     let repo_argument = {
-        let generic_id: ::syn::Path = ::syn::parse_quote!(id<Self>);
+        let generic_id: ::syn::Path = ::syn::parse_quote!(id<Self, Collection>);
         generic_id.segments.last().unwrap().arguments.clone()
     };
     for p in packages.0.iter_mut() {
diff --git a/bok-utils/src/main.rs b/bok-utils/src/main.rs
index fedb1d5..695cd3b 100644
--- a/bok-utils/src/main.rs
+++ b/bok-utils/src/main.rs
@@ -16,6 +16,7 @@
  */
 
 mod conf;
+//mod expanded;
 mod repos;
 
 fn main() {
diff --git a/bok-utils/src/repos/pkgs/one.rs b/bok-utils/src/repos/pkgs/one.rs
index f4f25e6..d9f8df4 100644
--- a/bok-utils/src/repos/pkgs/one.rs
+++ b/bok-utils/src/repos/pkgs/one.rs
@@ -32,6 +32,7 @@ impl ::std::default::Default for One {
         One {
             _bok_base: ::std::marker::PhantomData::default(),
             _bok_repo: ::std::marker::PhantomData::default(),
+            _bok_collection: ::std::marker::PhantomData::default(),
             my_attr: 1,
             version: ::bok::Version {
                 major: 0,
diff --git a/bok-utils/src/repos/pkgs/three.rs b/bok-utils/src/repos/pkgs/three.rs
index 57a0f1f..217790f 100644
--- a/bok-utils/src/repos/pkgs/three.rs
+++ b/bok-utils/src/repos/pkgs/three.rs
@@ -22,14 +22,13 @@ pub struct Three {
     pub my_attr: u32,
 }
 
-impl<R> ::std::default::Default for Three<R>
-where
-    R: ::bok::Repository,
-{
+#[::bok::package_impl]
+impl ::std::default::Default for Three {
     fn default() -> Self {
         Three {
             _bok_base: ::std::marker::PhantomData::default(),
             _bok_repo: ::std::marker::PhantomData::default(),
+            _bok_collection: ::std::marker::PhantomData::default(),
             version: ::bok::Version {
                 major: 0,
                 minor: 0,
diff --git a/bok-utils/src/repos/pkgs/two.rs b/bok-utils/src/repos/pkgs/two.rs
index 92d663e..5e9cd6c 100644
--- a/bok-utils/src/repos/pkgs/two.rs
+++ b/bok-utils/src/repos/pkgs/two.rs
@@ -28,6 +28,7 @@ impl ::std::default::Default for Two {
         Two {
             _bok_base: ::std::marker::PhantomData::default(),
             _bok_repo: ::std::marker::PhantomData::default(),
+            _bok_collection: ::std::marker::PhantomData::default(),
             my_attr: 2,
             my_attr2: 2,
             version: ::bok::Version {
diff --git a/bok/src/collection.rs b/bok/src/collection.rs
index 6a7b629..2b4690c 100644
--- a/bok/src/collection.rs
+++ b/bok/src/collection.rs
@@ -33,7 +33,7 @@ pub type PkgMap =
     BTreeMap<Path<PkgName>, (Arc<dyn Repository>, ArcLock<dyn PkgBuilder>)>;
 */
 
-pub trait Collection: ::std::any::Any {
+pub trait Collection: ::std::any::Any + ::core::fmt::Debug {
     fn as_any(&self) -> &dyn ::std::any::Any;
     fn as_any_mut(&mut self) -> &mut dyn ::std::any::Any;
 }