diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4315dfc..c53f4c1 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,6 +26,7 @@ jobs:
         with:
           profile: minimal
           toolchain: ${{ matrix.rust }}
+          components: rustfmt, clippy
           override: true
       - name: Test
         run: |
diff --git a/Cargo.toml b/Cargo.toml
index a7a3d40..e6785c6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,7 +9,8 @@ license = "Apache-2.0 OR MIT"
 repository = "https://github.com/trussed-dev/apdu-dispatch"
 
 [workspace.dependencies]
-iso7816 = "0.1.2"
+iso7816 = "0.2.0"
+heapless = "0.9"
 
 [patch.crates-io]
 apdu-app.path = "app"
diff --git a/app/Cargo.toml b/app/Cargo.toml
index c6b7823..48f5571 100644
--- a/app/Cargo.toml
+++ b/app/Cargo.toml
@@ -10,3 +10,4 @@ repository.workspace = true
 
 [dependencies]
 iso7816.workspace = true
+heapless.workspace = true
diff --git a/app/src/lib.rs b/app/src/lib.rs
index f04f60c..c30d7e1 100644
--- a/app/src/lib.rs
+++ b/app/src/lib.rs
@@ -1,11 +1,12 @@
 #![no_std]
 
-pub use iso7816::{command::CommandView, Data, Interface, Status};
+pub use heapless::VecView;
+pub use iso7816::{command::CommandView, Interface};
 
 pub type Result = iso7816::Result<()>;
 
 /// An App can receive and respond APDUs at behest of the ApduDispatch.
-pub trait App<const R: usize>: iso7816::App {
+pub trait App: iso7816::App {
     /// Given parsed APDU for select command.
     /// Write response data back to buf, and return length of payload.  Return APDU Error code on error.
     /// Alternatively, the app can defer the response until later by returning it in `poll()`.
@@ -13,7 +14,7 @@ pub trait App<const R: usize>: iso7816::App {
         &mut self,
         interface: Interface,
         apdu: CommandView<'_>,
-        reply: &mut Data<R>,
+        reply: &mut VecView<u8>,
     ) -> Result;
 
     /// Deselects the app. This is the result of another app getting selected.
@@ -22,5 +23,10 @@ pub trait App<const R: usize>: iso7816::App {
 
     /// Given parsed APDU for app when selected.
     /// Write response data back to buf, and return length of payload.  Return APDU Error code on error.
-    fn call(&mut self, interface: Interface, apdu: CommandView<'_>, reply: &mut Data<R>) -> Result;
+    fn call(
+        &mut self,
+        interface: Interface,
+        apdu: CommandView<'_>,
+        reply: &mut VecView<u8>,
+    ) -> Result;
 }
diff --git a/dispatch/Cargo.toml b/dispatch/Cargo.toml
index 18c7446..45c5b4b 100644
--- a/dispatch/Cargo.toml
+++ b/dispatch/Cargo.toml
@@ -11,9 +11,9 @@ repository.workspace = true
 [dependencies]
 apdu-app = "0.1.0"
 delog = "0.1.4"
-heapless = "0.7"
 interchange = "0.3.0"
 iso7816.workspace = true
+heapless.workspace = true
 
 [dev-dependencies]
 # Testing
diff --git a/dispatch/src/dispatch.rs b/dispatch/src/dispatch.rs
index 1a9e1ef..c795594 100644
--- a/dispatch/src/dispatch.rs
+++ b/dispatch/src/dispatch.rs
@@ -8,7 +8,6 @@
 //!
 //! Apps need to implement the App trait to be managed.
 //!
-use core::mem;
 
 use crate::response::SIZE as ResponseSize;
 use crate::App;
@@ -123,8 +122,8 @@ impl<'pipe> ApduDispatch<'pipe> {
     // but that won't work due to ownership rules
     fn find_app<'a, 'b>(
         aid: Option<&Aid>,
-        apps: &'a mut [&'b mut dyn App<ResponseSize>],
-    ) -> Option<&'a mut &'b mut dyn App<ResponseSize>> {
+        apps: &'a mut [&'b mut dyn App],
+    ) -> Option<&'a mut &'b mut dyn App> {
         // match aid {
         //     Some(aid) => apps.iter_mut().find(|app| aid.starts_with(app.rid())),
         //     None => None,
@@ -366,12 +365,7 @@ impl<'pipe> ApduDispatch<'pipe> {
     }
 
     #[inline(never)]
-    fn handle_app_select(
-        &mut self,
-        apps: &mut [&mut dyn App<ResponseSize>],
-        aid: Aid,
-        interface: Interface,
-    ) {
+    fn handle_app_select(&mut self, apps: &mut [&mut dyn App], aid: Aid, interface: Interface) {
         // three cases:
         // - currently selected app has different AID -> deselect it, to give it
         //   the chance to clear sensitive state
@@ -395,7 +389,7 @@ impl<'pipe> ApduDispatch<'pipe> {
                 _ => panic!("Unexpected buffer state."),
             };
 
-            let old_aid = mem::replace(&mut self.current_aid, Some(aid));
+            let old_aid = self.current_aid.replace(aid);
             if let Some(old_aid) = old_aid {
                 if old_aid != aid {
                     let app = Self::find_app(self.current_aid.as_ref(), apps).unwrap();
@@ -412,11 +406,7 @@ impl<'pipe> ApduDispatch<'pipe> {
     }
 
     #[inline(never)]
-    fn handle_app_command(
-        &mut self,
-        apps: &mut [&mut dyn App<ResponseSize>],
-        interface: Interface,
-    ) {
+    fn handle_app_command(&mut self, apps: &mut [&mut dyn App], interface: Interface) {
         // if there is a selected app, send it the command
         let mut response = response::Data::new();
         if let Some(app) = Self::find_app(self.current_aid.as_ref(), apps) {
@@ -431,7 +421,7 @@ impl<'pipe> ApduDispatch<'pipe> {
         };
     }
 
-    pub fn poll(&mut self, apps: &mut [&mut dyn App<ResponseSize>]) -> Option<Interface> {
+    pub fn poll(&mut self, apps: &mut [&mut dyn App]) -> Option<Interface> {
         // Only take on one transaction at a time.
         let request_type = self.check_for_request();
 
diff --git a/dispatch/tests/dispatch.rs b/dispatch/tests/dispatch.rs
index 236d34b..bc51927 100644
--- a/dispatch/tests/dispatch.rs
+++ b/dispatch/tests/dispatch.rs
@@ -1,6 +1,7 @@
 use apdu_dispatch::app::{App, CommandView, Result as AppResult};
 use apdu_dispatch::dispatch;
 use apdu_dispatch::{interchanges, response};
+use heapless::VecView;
 use hex_literal::hex;
 use interchange::Channel;
 use iso7816::Status;
@@ -47,12 +48,12 @@ impl iso7816::App for TestApp1 {
 }
 
 // This app echos to Ins code 0x10
-impl App<{ apdu_dispatch::response::SIZE }> for TestApp1 {
+impl App for TestApp1 {
     fn select(
         &mut self,
         _interface: dispatch::Interface,
         _apdu: CommandView<'_>,
-        _reply: &mut response::Data,
+        _reply: &mut VecView<u8>,
     ) -> AppResult {
         Ok(())
     }
@@ -63,7 +64,7 @@ impl App<{ apdu_dispatch::response::SIZE }> for TestApp1 {
         &mut self,
         _: dispatch::Interface,
         apdu: CommandView<'_>,
-        reply: &mut response::Data,
+        reply: &mut VecView<u8>,
     ) -> AppResult {
         println!("TestApp1::call");
         match apdu.instruction().into() {
@@ -79,8 +80,8 @@ impl App<{ apdu_dispatch::response::SIZE }> for TestApp1 {
             }
             // For measuring the stack burden of dispatch
             0x15 => {
-                let buf = heapless::Vec::new();
-                let addr = (&buf as *const response::Data) as u32;
+                let buf = heapless::Vec::<u8, { response::SIZE }>::new();
+                let addr = (&buf as *const VecView<u8>).addr() as u32;
                 reply.extend_from_slice(&addr.to_be_bytes()).unwrap();
                 Ok(())
             }
@@ -122,12 +123,12 @@ impl iso7816::App for TestApp2 {
 }
 
 // This app echos to Ins code 0x20
-impl App<{ apdu_dispatch::response::SIZE }> for TestApp2 {
+impl App for TestApp2 {
     fn select(
         &mut self,
         _interface: dispatch::Interface,
         _apdu: CommandView<'_>,
-        _reply: &mut response::Data,
+        _reply: &mut VecView<u8>,
     ) -> AppResult {
         Ok(())
     }
@@ -138,7 +139,7 @@ impl App<{ apdu_dispatch::response::SIZE }> for TestApp2 {
         &mut self,
         _: dispatch::Interface,
         apdu: CommandView<'_>,
-        reply: &mut response::Data,
+        reply: &mut VecView<u8>,
     ) -> AppResult {
         println!("TestApp2::call");
         match apdu.instruction().into() {
@@ -174,12 +175,12 @@ impl iso7816::App for PanicApp {
 }
 
 // This app echos to Ins code 0x20
-impl App<{ apdu_dispatch::response::SIZE }> for PanicApp {
+impl App for PanicApp {
     fn select(
         &mut self,
         _interface: dispatch::Interface,
         _apdu: CommandView<'_>,
-        _reply: &mut response::Data,
+        _reply: &mut VecView<u8>,
     ) -> AppResult {
         panic!("Dont call the panic app");
     }
@@ -192,7 +193,7 @@ impl App<{ apdu_dispatch::response::SIZE }> for PanicApp {
         &mut self,
         _: dispatch::Interface,
         _apdu: CommandView<'_>,
-        _reply: &mut response::Data,
+        _reply: &mut VecView<u8>,
     ) -> AppResult {
         panic!("Dont call the panic app");
     }
diff --git a/fuzz/Cargo.toml b/fuzz/Cargo.toml
index b3b6356..a271373 100644
--- a/fuzz/Cargo.toml
+++ b/fuzz/Cargo.toml
@@ -12,6 +12,7 @@ cargo-fuzz = true
 libfuzzer-sys = "0.4"
 arbitrary = { version = "1", features = ["derive"] }
 interchange = "0.3.0"
+heapless = "0.9.0"
 
 [dependencies.apdu-dispatch]
 path = "../dispatch"
diff --git a/fuzz/fuzz_targets/fuzz_target_1.rs b/fuzz/fuzz_targets/fuzz_target_1.rs
index 924c6f0..33d718f 100644
--- a/fuzz/fuzz_targets/fuzz_target_1.rs
+++ b/fuzz/fuzz_targets/fuzz_target_1.rs
@@ -2,6 +2,7 @@
 use apdu_dispatch::app::Result as AppResult;
 use apdu_dispatch::{dispatch::Interface, interchanges, iso7816, App};
 use arbitrary::{Arbitrary, Unstructured};
+use heapless::VecView;
 use interchange::Channel;
 use libfuzzer_sys::fuzz_target;
 
@@ -53,12 +54,12 @@ impl iso7816::App for FuzzAppImpl {
     }
 }
 
-impl App<{ apdu_dispatch::response::SIZE }> for FuzzAppImpl {
+impl App for FuzzAppImpl {
     fn select(
         &mut self,
         _interface: iso7816::Interface,
         _apdu: apdu_dispatch::app::CommandView<'_>,
-        _reply: &mut apdu_dispatch::response::Data,
+        _reply: &mut heapless::VecView<u8>,
     ) -> AppResult {
         Ok(())
     }
@@ -69,7 +70,7 @@ impl App<{ apdu_dispatch::response::SIZE }> for FuzzAppImpl {
         &mut self,
         _: Interface,
         _apdu: apdu_dispatch::app::CommandView<'_>,
-        reply: &mut apdu_dispatch::response::Data,
+        reply: &mut VecView<u8>,
     ) -> AppResult {
         let (ref data, status) = &self.responses[self.count];
         reply.extend_from_slice(data).ok();
@@ -89,10 +90,7 @@ fuzz_target!(|input: Input| {
         .enumerate()
         .map(|(idx, app)| FuzzAppImpl::new(idx, app))
         .collect();
-    let mut dyn_apps: Vec<_> = apps
-        .iter_mut()
-        .map(|s| (s as &mut dyn apdu_dispatch::App<7609>))
-        .collect();
+    let mut dyn_apps: Vec<&mut dyn apdu_dispatch::App> = apps.iter_mut().map(|s| s as _).collect();
 
     let contact = Channel::new();
     let (mut contact_requester, contact_responder) = contact