diff --git a/app/src/commands/attestation.rs b/app/src/commands/attestation.rs
index 0a9fb15c..78b22173 100644
--- a/app/src/commands/attestation.rs
+++ b/app/src/commands/attestation.rs
@@ -1,10 +1,12 @@
-use crate::opts::{EnclaveOpts, Opts};
+use crate::{
+    enclave::EnclaveLoader,
+    opts::{EnclaveOpts, Opts},
+};
 use anyhow::{bail, Result};
 use clap::Parser;
 use crypto::Address;
 use ecall_commands::IASRemoteAttestationInput;
 use enclave_api::{Enclave, EnclaveCommandAPI, EnclaveProtoAPI};
-use std::path::PathBuf;
 use store::transaction::CommitStore;
 
 /// `attestation` subcommand
@@ -19,14 +21,11 @@ pub enum AttestationCmd {
 }
 
 impl AttestationCmd {
-    pub fn run<S>(
-        &self,
-        opts: &Opts,
-        enclave_loader: impl FnOnce(&Opts, Option<&PathBuf>, bool) -> Result<Enclave<S>>,
-    ) -> Result<()>
+    pub fn run<S, L>(&self, opts: &Opts, enclave_loader: L) -> Result<()>
     where
         S: CommitStore,
         Enclave<S>: EnclaveProtoAPI<S>,
+        L: EnclaveLoader<S>,
     {
         let home = opts.get_home();
         match self {
@@ -35,7 +34,7 @@ impl AttestationCmd {
                     bail!("home directory doesn't exist at {:?}", home);
                 }
                 run_ias_remote_attestation(
-                    enclave_loader(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
+                    enclave_loader.load(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
                     cmd,
                 )
             }
@@ -45,7 +44,7 @@ impl AttestationCmd {
                     bail!("home directory doesn't exist at {:?}", home);
                 }
                 run_simulate_remote_attestation(
-                    enclave_loader(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
+                    enclave_loader.load(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
                     cmd,
                 )
             }
@@ -102,14 +101,14 @@ pub struct SimulateRemoteAttestation {
         long = "signing_cert_path",
         help = "Path to a der-encoded file that contains X.509 certificate"
     )]
-    pub signing_cert_path: PathBuf,
+    pub signing_cert_path: std::path::PathBuf,
 
     /// Path to a PEM-encoded file that contains PKCS#8 private key
     #[clap(
         long = "signing_key",
         help = "Path to a PEM-encoded file that contains PKCS#8 private key"
     )]
-    pub signing_key_path: PathBuf,
+    pub signing_key_path: std::path::PathBuf,
 
     /// Validate a signing certificate using openssl command
     #[clap(
diff --git a/app/src/commands/elc.rs b/app/src/commands/elc.rs
index 2bf48219..07aa0f86 100644
--- a/app/src/commands/elc.rs
+++ b/app/src/commands/elc.rs
@@ -1,4 +1,7 @@
-use crate::opts::{EnclaveOpts, Opts};
+use crate::{
+    enclave::EnclaveLoader,
+    opts::{EnclaveOpts, Opts},
+};
 use anyhow::Result;
 use clap::Parser;
 use enclave_api::{Enclave, EnclaveProtoAPI};
@@ -42,17 +45,15 @@ impl ELCOpts {
 }
 
 impl ELCCmd {
-    pub fn run<S>(
-        &self,
-        opts: &Opts,
-        enclave_loader: impl FnOnce(&Opts, Option<&PathBuf>, bool) -> Result<Enclave<S>>,
-    ) -> Result<()>
+    pub fn run<S, L>(&self, opts: &Opts, enclave_loader: L) -> Result<()>
     where
         S: CommitStore,
         Enclave<S>: EnclaveProtoAPI<S>,
+        L: EnclaveLoader<S>,
     {
         let elc_opts = self.opts();
-        let enclave = enclave_loader(opts, elc_opts.enclave.path.as_ref(), elc_opts.enclave.debug)?;
+        let enclave =
+            enclave_loader.load(opts, elc_opts.enclave.path.as_ref(), elc_opts.enclave.debug)?;
         match self {
             Self::CreateClient(_) => {
                 let _ = enclave.proto_create_client(elc_opts.load()?)?;
diff --git a/app/src/commands/enclave.rs b/app/src/commands/enclave.rs
index 5e27dda3..224b1b1f 100644
--- a/app/src/commands/enclave.rs
+++ b/app/src/commands/enclave.rs
@@ -1,4 +1,7 @@
-use crate::opts::{EnclaveOpts, Opts};
+use crate::{
+    enclave::EnclaveLoader,
+    opts::{EnclaveOpts, Opts},
+};
 use anyhow::{anyhow, Result};
 use clap::Parser;
 use ecall_commands::GenerateEnclaveKeyInput;
@@ -6,7 +9,6 @@ use enclave_api::{Enclave, EnclaveCommandAPI, EnclaveProtoAPI};
 use lcp_types::Mrenclave;
 use log::*;
 use serde_json::json;
-use std::path::PathBuf;
 use store::transaction::CommitStore;
 
 // `enclave` subcommand
@@ -23,14 +25,11 @@ pub enum EnclaveCmd {
 }
 
 impl EnclaveCmd {
-    pub fn run<S>(
-        &self,
-        opts: &Opts,
-        enclave_loader: impl FnOnce(&Opts, Option<&PathBuf>, bool) -> Result<Enclave<S>>,
-    ) -> Result<()>
+    pub fn run<S, L>(&self, opts: &Opts, enclave_loader: L) -> Result<()>
     where
         S: CommitStore,
         Enclave<S>: EnclaveProtoAPI<S>,
+        L: EnclaveLoader<S>,
     {
         let home = opts.get_home();
         if !home.exists() {
@@ -39,15 +38,15 @@ impl EnclaveCmd {
         }
         match self {
             Self::GenerateKey(cmd) => run_generate_key(
-                enclave_loader(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
+                enclave_loader.load(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
                 cmd,
             ),
             Self::ListKeys(cmd) => run_list_keys(
-                enclave_loader(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
+                enclave_loader.load(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
                 cmd,
             ),
             Self::PruneKeys(cmd) => run_prune_keys(
-                enclave_loader(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
+                enclave_loader.load(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?,
                 cmd,
             ),
             Self::Metadata(cmd) => run_print_metadata(opts, cmd),
diff --git a/app/src/commands/service.rs b/app/src/commands/service.rs
index 9fc04fbd..0f5a81ae 100644
--- a/app/src/commands/service.rs
+++ b/app/src/commands/service.rs
@@ -1,10 +1,10 @@
+use crate::enclave::EnclaveLoader;
 use crate::opts::{EnclaveOpts, Opts};
 use anyhow::Result;
 use clap::Parser;
 use enclave_api::{Enclave, EnclaveProtoAPI};
 use log::*;
 use service::{run_service, AppService};
-use std::path::PathBuf;
 use std::sync::Arc;
 use store::transaction::CommitStore;
 use tokio::runtime::Builder;
@@ -38,19 +38,17 @@ pub struct Start {
 }
 
 impl ServiceCmd {
-    pub fn run<S>(
-        &self,
-        opts: &Opts,
-        enclave_loader: impl FnOnce(&Opts, Option<&PathBuf>, bool) -> Result<Enclave<S>>,
-    ) -> Result<()>
+    pub fn run<S, L>(&self, opts: &Opts, enclave_loader: L) -> Result<()>
     where
         S: CommitStore + 'static,
         Enclave<S>: EnclaveProtoAPI<S>,
+        L: EnclaveLoader<S>,
     {
         match self {
             Self::Start(cmd) => {
                 let addr = cmd.address.parse()?;
-                let enclave = enclave_loader(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?;
+                let enclave =
+                    enclave_loader.load(opts, cmd.enclave.path.as_ref(), cmd.enclave.debug)?;
 
                 let mut rb = Builder::new_multi_thread();
                 let rb = if let Some(threads) = cmd.threads {
diff --git a/app/src/enclave.rs b/app/src/enclave.rs
index 6984be32..706bceda 100644
--- a/app/src/enclave.rs
+++ b/app/src/enclave.rs
@@ -5,12 +5,18 @@ use keymanager::EnclaveKeyManager;
 use std::path::PathBuf;
 use store::transaction::CommitStore;
 
-pub(crate) fn build_enclave_loader<S: CommitStore>(
-) -> impl FnOnce(&Opts, Option<&PathBuf>, bool) -> Result<Enclave<S>>
+pub trait EnclaveLoader<S: CommitStore> {
+    fn load(&self, opts: &Opts, path: Option<&PathBuf>, debug: bool) -> Result<Enclave<S>>;
+}
+
+#[derive(Debug)]
+pub struct DefaultEnclaveLoader<S: CommitStore>(std::marker::PhantomData<S>);
+
+impl<S: CommitStore> EnclaveLoader<S> for DefaultEnclaveLoader<S>
 where
     Enclave<S>: EnclaveProtoAPI<S>,
 {
-    |opts, path, debug| {
+    fn load(&self, opts: &Opts, path: Option<&PathBuf>, debug: bool) -> Result<Enclave<S>> {
         let path = if let Some(path) = path {
             path.clone()
         } else {
@@ -30,3 +36,10 @@ where
         }
     }
 }
+
+pub const fn build_enclave_loader<S: CommitStore>() -> DefaultEnclaveLoader<S>
+where
+    Enclave<S>: EnclaveProtoAPI<S>,
+{
+    DefaultEnclaveLoader(std::marker::PhantomData)
+}