diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 9f5624eb0f1..c584a2c0850 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -75,14 +75,13 @@ fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Ve
             self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
 
         let mut arg_tys = vec![];
-        let parameters = Substitution::builder(num_args)
+        let arg_ty = TyBuilder::tuple(num_args)
             .fill(repeat_with(|| {
                 let arg = self.table.new_type_var();
                 arg_tys.push(arg.clone());
                 arg
             }))
             .build();
-        let arg_ty = TyKind::Tuple(num_args, parameters).intern(&Interner);
 
         let projection = {
             let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index c9219776bde..d55ae49005a 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -93,16 +93,13 @@ fn resolve_value_path(
             ValueNs::GenericParam(it) => return Some(self.db.const_param_ty(it)),
         };
 
-        let ty = self.db.value_ty(typable);
-        // self_subst is just for the parent
         let parent_substs = self_subst.unwrap_or_else(|| Substitution::empty(&Interner));
         let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
         let substs = ctx.substs_from_path(path, typable, true);
-        let full_substs = Substitution::builder(substs.len(&Interner))
+        let ty = TyBuilder::value_ty(self.db, typable)
             .use_parent_substs(&parent_substs)
             .fill(substs.interned(&Interner)[parent_substs.len(&Interner)..].iter().cloned())
             .build();
-        let ty = ty.subst(&full_substs);
         Some(ty)
     }
 
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index d2496db3ba4..a04b935ef9f 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -186,14 +186,11 @@ pub(crate) fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substitution> {
             );
         }
     }
-    Some(
-        Substitution::builder(tys.binders.len(&Interner))
-            .fill(
-                vars.iter(&Interner)
-                    .map(|v| table.resolve_ty_completely(v.assert_ty_ref(&Interner).clone())),
-            )
-            .build(),
-    )
+    Some(Substitution::from_iter(
+        &Interner,
+        vars.iter(&Interner)
+            .map(|v| table.resolve_ty_completely(v.assert_ty_ref(&Interner).clone())),
+    ))
 }
 
 #[derive(Clone, Debug)]
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 27ebb7b7cd3..f99b70f2b94 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -492,10 +492,6 @@ pub(crate) fn bound_vars(generic_params: &Generics, debruijn: DebruijnIndex) ->
                 .map(|(idx, _)| TyKind::BoundVar(BoundVar::new(debruijn, idx)).intern(&Interner)),
         )
     }
-
-    fn builder(param_count: usize) -> SubstsBuilder {
-        SubstsBuilder { vec: Vec::with_capacity(param_count), param_count }
-    }
 }
 
 /// Return an index of a parameter in the generic type parameter list by it's id.
@@ -503,52 +499,6 @@ pub fn param_idx(db: &dyn HirDatabase, id: TypeParamId) -> Option<usize> {
     generics(db.upcast(), id.parent).param_idx(id)
 }
 
-#[derive(Debug, Clone)]
-pub struct SubstsBuilder {
-    vec: Vec<GenericArg>,
-    param_count: usize,
-}
-
-impl SubstsBuilder {
-    pub fn build(self) -> Substitution {
-        assert_eq!(self.vec.len(), self.param_count);
-        Substitution::from_iter(&Interner, self.vec)
-    }
-
-    pub fn push(mut self, ty: impl CastTo<GenericArg>) -> Self {
-        self.vec.push(ty.cast(&Interner));
-        self
-    }
-
-    fn remaining(&self) -> usize {
-        self.param_count - self.vec.len()
-    }
-
-    pub fn fill_with_bound_vars(self, debruijn: DebruijnIndex, starting_from: usize) -> Self {
-        self.fill(
-            (starting_from..)
-                .map(|idx| TyKind::BoundVar(BoundVar::new(debruijn, idx)).intern(&Interner)),
-        )
-    }
-
-    pub fn fill_with_unknown(self) -> Self {
-        self.fill(iter::repeat(TyKind::Unknown.intern(&Interner)))
-    }
-
-    pub fn fill(mut self, filler: impl Iterator<Item = impl CastTo<GenericArg>>) -> Self {
-        self.vec.extend(filler.take(self.remaining()).casted(&Interner));
-        assert_eq!(self.remaining(), 0);
-        self
-    }
-
-    pub fn use_parent_substs(mut self, parent_substs: &Substitution) -> Self {
-        assert!(self.vec.is_empty());
-        assert!(parent_substs.len(&Interner) <= self.param_count);
-        self.vec.extend(parent_substs.iter(&Interner).cloned());
-        self
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
 pub struct Binders<T> {
     pub num_binders: usize,
@@ -921,6 +871,18 @@ pub fn build(self) -> Ty {
     }
 }
 
+struct Tuple(usize);
+impl TyBuilder<Tuple> {
+    pub fn tuple(size: usize) -> TyBuilder<Tuple> {
+        TyBuilder::new(Tuple(size), size)
+    }
+
+    pub fn build(self) -> Ty {
+        let (Tuple(size), subst) = self.build_internal();
+        TyKind::Tuple(size, subst).intern(&Interner)
+    }
+}
+
 impl TyBuilder<TraitId> {
     pub fn trait_ref(db: &dyn HirDatabase, trait_id: TraitId) -> TyBuilder<TraitId> {
         let generics = generics(db.upcast(), trait_id.into());
@@ -970,6 +932,10 @@ pub fn def_ty(db: &dyn HirDatabase, def: TyDefId) -> TyBuilder<Binders<Ty>> {
     pub fn impl_self_ty(db: &dyn HirDatabase, def: hir_def::ImplId) -> TyBuilder<Binders<Ty>> {
         TyBuilder::subst_binders(db.impl_self_ty(def))
     }
+
+    pub fn value_ty(db: &dyn HirDatabase, def: ValueTyDefId) -> TyBuilder<Binders<Ty>> {
+        TyBuilder::subst_binders(db.value_ty(def))
+    }
 }
 
 impl Ty {