diff --git a/src/corpus/mod.rs b/src/corpus/mod.rs
index 2b13225a7e..aa43f1d628 100644
--- a/src/corpus/mod.rs
+++ b/src/corpus/mod.rs
@@ -1,55 +1,37 @@
 pub mod testcase;
-pub use testcase::{Testcase, SimpleTestcase};
+pub use testcase::Testcase;
 
-use crate::utils::Rand;
+use crate::utils::{Rand, HasRand};
+use crate::inputs::Input;
 use crate::AflError;
 
 use std::path::PathBuf;
 
+pub trait HasEntriesVec<InputT: Input> {
+    /// Get the entries vector field
+    fn entries(&self) -> &Vec<Box<Testcase<InputT>>>;
+
+    /// Get the entries vector field (mutable)
+    fn entries_mut(&mut self) -> &mut Vec<Box<Testcase<InputT>>>;
+}
+
 /// Corpus with all current testcases
-pub trait Corpus {
-    /// Returns the number of elements
-    fn count(&self) -> usize;
-
-    fn add(&mut self, entry: Box<dyn Testcase>);
-
-    /// Removes an entry from the corpus, returning it if it was present.
-    fn remove(&mut self, entry: &dyn Testcase) -> Option<Box<dyn Testcase>>;
-
-    /// Gets a random entry
-    fn random_entry(&mut self) -> Result<&Box<dyn Testcase>, AflError>;
-
-    /// Gets the next entry
-    fn get(&mut self) -> Result<&Box<dyn Testcase>, AflError>;
-}
-
-pub struct BaseCorpus<'a, RandT: Rand> {
-    rand: &'a mut RandT,
-    entries: Vec<Box<dyn Testcase>>,
-    dir_path: PathBuf,
-}
-
-impl<RandT: Rand> Corpus for BaseCorpus<'_, RandT> {
+pub trait Corpus<InputT: Input, RandT: Rand> : HasEntriesVec<InputT> + HasRand<RandT> {
     /// Returns the number of elements
     fn count(&self) -> usize {
-        self.entries.len()
+        self.entries().len()
     }
 
-    fn add(&mut self, mut entry: Box<dyn Testcase>) {
-        if entry.get_filename() == None {
-            // TODO walk entry metadatas to ask for pices of filename (e.g. :havoc in AFL)
-            let filename = &(String::from("id:") + &self.entries.len().to_string());
-            let filename = self.dir_path.join(filename);
-            entry.set_filename(filename);
-        }
-        self.entries.push(entry);
+    /// Add an entry to the corpus
+    fn add(&mut self, mut entry: Box<Testcase<InputT>>) {
+        self.entries_mut().push(entry);
     }
 
     /// Removes an entry from the corpus, returning it if it was present.
-    fn remove(&mut self, entry: &dyn Testcase) -> Option<Box<dyn Testcase>> {
+    fn remove(&mut self, entry: &Testcase<InputT>) -> Option<Box<Testcase<InputT>>> {
         let mut i: usize = 0;
         let mut found = false;
-        for x in &self.entries {
+        for x in self.entries() {
             i = i + 1;
             if x.as_ref() as *const _ == entry as *const _ {
                 found = true;
@@ -59,24 +41,99 @@ impl<RandT: Rand> Corpus for BaseCorpus<'_, RandT> {
         if !found {
             return None;
         }
-        Some(self.entries.remove(i))
+        Some(self.entries_mut().remove(i))
     }
 
     /// Gets a random entry
-    fn random_entry(&mut self) -> Result<&Box<dyn Testcase>, AflError> {
-        let id = self.rand.below(self.entries.len() as u64) as usize;
-        Ok(self.entries.get_mut(id).unwrap())
+    fn random_entry(&mut self) -> Result<&Box<Testcase<InputT>>, AflError> {
+        let id = self.rand_mut().below(self.entries().len() as u64) as usize;
+        Ok(self.entries_mut().get_mut(id).unwrap())
     }
 
-    /// Gets the next entry
-    fn get(&mut self) -> Result<&Box<dyn Testcase>, AflError> {
+    /// Gets the next entry (random by default)
+    fn get(&mut self) -> Result<&Box<Testcase<InputT>>, AflError> {
         self.random_entry()
     }
 }
 
-impl<RandT: Rand> BaseCorpus<'_, RandT> {
-    pub fn new<'a>(rand: &'a mut RandT, dir_path: PathBuf) -> BaseCorpus<'a, RandT> {
-        BaseCorpus {
+pub struct InMemoryCorpus<'a, InputT: Input, RandT: Rand> {
+    rand: &'a mut RandT,
+    entries: Vec<Box<Testcase<InputT>>>,
+}
+
+impl<InputT: Input, RandT: Rand> HasEntriesVec<InputT> for InMemoryCorpus<'_, InputT, RandT> {
+    fn entries(&self) -> &Vec<Box<Testcase<InputT>>> {
+        &self.entries
+    }
+    fn entries_mut(&mut self) -> &mut Vec<Box<Testcase<InputT>>>{
+        &mut self.entries
+    }
+}
+
+impl<InputT: Input, RandT: Rand> HasRand<RandT> for InMemoryCorpus<'_, InputT, RandT> {
+    fn rand(&self) -> &Box<dyn Rand> {
+        &self.rand
+    }
+    fn rand_mut(&mut self) -> &mut Box<dyn Rand> {
+        &mut self.rand
+    }
+}
+
+impl<InputT: Input, RandT: Rand> Corpus<InputT, RandT> for InMemoryCorpus<'_, InputT, RandT> {
+    // Just use the default implementation
+}
+
+impl<InputT: Input, RandT: Rand> InMemoryCorpus<'_, InputT, RandT> {
+    pub fn new<'a>(rand: &'a mut RandT) -> Self {
+        InMemoryCorpus {
+            rand: rand,
+            entries: vec![],
+        }
+    }
+}
+
+pub struct OnDiskCorpus<'a, InputT: Input, RandT: Rand> {
+    rand: &'a mut RandT,
+    entries: Vec<Box<Testcase<InputT>>>,
+    dir_path: PathBuf,
+}
+
+impl<InputT: Input, RandT: Rand> HasEntriesVec<InputT> for OnDiskCorpus<'_, InputT, RandT> {
+    fn entries(&self) -> &Vec<Box<Testcase<InputT>>> {
+        &self.entries
+    }
+    fn entries_mut(&mut self) -> &mut Vec<Box<Testcase<InputT>>>{
+        &mut self.entries
+    }
+}
+
+impl<InputT: Input, RandT: Rand> HasRand<RandT> for OnDiskCorpus<'_, InputT, RandT> {
+    fn rand(&self) -> &Box<dyn Rand> {
+        &self.rand
+    }
+    fn rand_mut(&mut self) -> &mut Box<dyn Rand> {
+        &mut self.rand
+    }
+}
+
+impl<InputT: Input, RandT: Rand> Corpus<InputT, RandT> for OnDiskCorpus<'_, InputT, RandT> {
+    /// Add an entry and save it to disk
+    fn add(&mut self, mut entry: Box<Testcase<InputT>>) {
+        if entry.filename() == None {
+            // TODO walk entry metadatas to ask for pices of filename (e.g. :havoc in AFL)
+            let filename = &(String::from("id:") + &self.entries.len().to_string());
+            let filename = self.dir_path.join(filename);
+            entry.filename_mut() = filename;
+        }
+        self.entries.push(entry);
+    }
+
+    // TODO save and remove files, cache, etc..., ATM use just InMemoryCorpus
+}
+
+impl<InputT: Input, RandT: Rand> OnDiskCorpus<'_, InputT, RandT> {
+    pub fn new<'a>(rand: &'a mut RandT, dir_path: PathBuf) -> Self {
+        OnDiskCorpus {
             dir_path: dir_path,
             entries: vec![],
             rand: rand,
@@ -84,35 +141,35 @@ impl<RandT: Rand> BaseCorpus<'_, RandT> {
     }
 }
 
-/// A queue-like corpus
-pub struct QueueCorpus<'a, RandT: Rand> {
-    base: BaseCorpus<'a, RandT>,
+/// A Queue-like corpus, wrapping an existing Corpus instance
+pub struct QueueCorpus<'a, InputT: Input, RandT: Rand, CorpusT: Corpus<InputT, RandT>> {
+    corpus: CorpusT,
     pos: usize,
     cycles: u64,
 }
 
-impl<RandT: Rand> Corpus for QueueCorpus<'_, RandT> {
+impl<'a, InputT: Input, RandT: Rand, CorpusT: Corpus<InputT, RandT>> Corpus<InputT, RandT> for QueueCorpus<'_, InputT, RandT, CorpusT> {
     /// Returns the number of elements
     fn count(&self) -> usize {
-        self.base.count()
+        self.corpus.count()
     }
 
-    fn add(&mut self, entry: Box<dyn Testcase>) {
-        self.base.add(entry);
+    fn add(&mut self, entry: Box<Testcase<InputT>>) {
+        self.corpus.add(entry);
     }
 
     /// Removes an entry from the corpus, returning it if it was present.
-    fn remove(&mut self, entry: &dyn Testcase) -> Option<Box<dyn Testcase>> {
-        self.base.remove(entry)
+    fn remove(&mut self, entry: &Testcase<InputT>) -> Option<Box<Testcase<InputT>>> {
+        self.corpus.remove(entry)
     }
 
     /// Gets a random entry
-    fn random_entry(&mut self) -> Result<&Box<dyn Testcase>, AflError> {
-        self.base.random_entry()
+    fn random_entry(&mut self) -> Result<&Box<Testcase<InputT>>, AflError> {
+        self.corpus.random_entry()
     }
 
     /// Gets the next entry
-    fn get(&mut self) -> Result<&Box<dyn Testcase>, AflError> {
+    fn get(&mut self) -> Result<&Box<Testcase<InputT>>, AflError> {
         if self.count() == 0 {
             return Err(AflError::Empty("Testcases".to_string()));
         }
@@ -121,24 +178,24 @@ impl<RandT: Rand> Corpus for QueueCorpus<'_, RandT> {
             self.cycles = self.cycles + 1;
             self.pos = 0;
         }
-        Ok(self.base.entries.get_mut(self.pos).unwrap())
+        Ok(self.corpus.entries.get_mut(self.pos).unwrap())
     }
 }
 
-impl<RandT: Rand> QueueCorpus<'_, RandT> {
-    pub fn new<'a>(rand: &'a mut RandT, dir_path: PathBuf) -> QueueCorpus<'a, RandT> {
+impl<'a, InputT: Input, RandT: Rand, CorpusT: Corpus<InputT, RandT>> QueueCorpus<'_, InputT, RandT, CorpusT> {
+    pub fn new(corpus: CorpusT) -> Self {
         QueueCorpus {
-            base: BaseCorpus::new(rand, dir_path),
+            corpus: corpus,
             cycles: 0,
             pos: 0,
         }
     }
 
-    pub fn get_cycles(&self) -> u64 {
+    pub fn cycles(&self) -> u64 {
         self.cycles
     }
 
-    pub fn get_pos(&self) -> usize {
+    pub fn pos(&self) -> usize {
         self.pos
     }
 }
@@ -146,8 +203,7 @@ impl<RandT: Rand> QueueCorpus<'_, RandT> {
 #[cfg(test)]
 mod tests {
     use crate::corpus::Corpus;
-    use crate::corpus::QueueCorpus;
-    use crate::corpus::SimpleTestcase;
+    use crate::corpus::{QueueCorpus, OnDiskCorpus};
     use crate::corpus::Testcase;
     use crate::inputs::bytes::BytesInput;
     use crate::utils::Xoshiro256StarRand;
@@ -158,13 +214,13 @@ mod tests {
 
     fn test_queuecorpus() {
         let mut rand = Xoshiro256StarRand::new();
-        let mut q = QueueCorpus::new(&mut rand, PathBuf::from("fancy/path"));
+        let mut q = QueueCorpus::new(OnDiskCorpus::new(&mut rand, PathBuf::from("fancy/path")));
         let i = Box::new(BytesInput::new(vec![0; 4]));
-        let mut t = Box::new(SimpleTestcase::new(i));
+        let mut t = Box::new(Testcase::new(i));
         t.set_filename(PathBuf::from("fancyfile"));
         q.add(t);
         let filename = q.get().unwrap().get_filename().unwrap().to_owned();
         assert_eq!(filename, q.get().unwrap().get_filename().unwrap().to_owned());
-        assert_eq!(filename, PathBuf::from("fancyfile"));
+        assert_eq!(filename, PathBuf::from("fancy/path/fancyfile"));
     }
 }
diff --git a/src/corpus/testcase.rs b/src/corpus/testcase.rs
index 86384f1b5d..65328db237 100644
--- a/src/corpus/testcase.rs
+++ b/src/corpus/testcase.rs
@@ -6,63 +6,82 @@ use std::path::PathBuf;
 
 pub trait TestcaseMetadata {}
 
-pub trait Testcase {
+/*
+pub trait TestcaseTrait<InputT: Input> {
+    /// Make sure to return a valid input instance loading it from disk if not in memory
+    fn load_input(&mut self) -> Result<&Box<InputT>, AflError>;
 
-    fn load_input(&mut self) -> Result<&Box<dyn Input>, AflError>;
+    /// Get the input, if any
+    fn input(&self) -> &Option<Box<InputT>>;
 
-    fn get_input(&self) -> Option<& Box<dyn Input>>;
+    /// Get the input, if any (mutable)
+    fn input_mut(&mut self) -> &mut Option<Box<InputT>>;
 
-    fn is_on_disk(&self) -> bool;
+    /// Get the filename, if any
+    fn filename(&self) -> &Option<PathBuf>;
 
-    fn get_filename(&self) -> Option<& PathBuf>;
-
-    fn set_filename(&mut self, filename: PathBuf);
-
-    fn get_metadatas(&mut self) -> &mut HashMap<String, Box<dyn TestcaseMetadata>>;
+    /// Get the filename, if any (mutable)
+    fn filename_mut(&mut self, filename: PathBuf) -> &mut &Option<PathBuf>;
 
+    /// Get all the metadatas into an HashMap
+    fn metadatas(&mut self) -> &mut HashMap<String, Box<dyn TestcaseMetadata>>;
 }
+*/
 
 #[derive(Default)]
-pub struct SimpleTestcase {
-    input: Option<Box<dyn Input>>,
-    // is_on_disk: bool, // not needed, look at the Option
+pub struct Testcase<InputT: Input> {
+    input: Option<Box<InputT>>,
     filename: Option<PathBuf>,
     metadatas: HashMap<String, Box<dyn TestcaseMetadata>>,
 }
 
-impl Testcase for SimpleTestcase {
-    fn load_input(&mut self) -> Result<&Box<dyn Input>, AflError> {
+impl<InputT: Input> Testcase<InputT> {
+    /// Make sure to return a valid input instance loading it from disk if not in memory
+    pub fn load_input(&mut self) -> Result<&Box<InputT>, AflError> {
         // TODO: Implement cache to disk
         self.input.as_ref().ok_or(AflError::NotImplemented("load_input".to_string()))
     }
 
-    fn get_input(&self) -> Option<& Box<dyn Input>> {
-        self.input.as_ref()
+    /// Get the input, if any
+    pub fn input(&self) -> &Option<Box<InputT>> {
+        &self.input
     }
 
-    fn is_on_disk(&self) -> bool {
-        !self.input.is_some() && self.filename.is_some()
+    /// Get the input, if any (mutable)
+    pub fn input_mut(&mut self) -> &mut Option<Box<InputT>> {
+        &mut self.input
     }
 
-    fn get_filename(&self) -> Option<& PathBuf> {
-        self.filename.as_ref()
+    /// Get the filename, if any
+    pub fn filename(&self) -> &Option<PathBuf> {
+        &self.filename
     }
 
-    fn set_filename(&mut self, filename: PathBuf) {
-        self.filename = Some(filename)
+    /// Get the filename, if any (mutable)
+    pub fn filename_mut(&mut self, filename: PathBuf) -> &mut Option<PathBuf> {
+        &mut self.filename
     }
 
-    fn get_metadatas(&mut self) -> &mut HashMap<String, Box<dyn TestcaseMetadata>> {
+    /// Get all the metadatas into an HashMap
+    pub fn metadatas(&mut self) -> &mut HashMap<String, Box<dyn TestcaseMetadata>> {
         &mut self.metadatas
     }
-}
 
-impl SimpleTestcase {
-    pub fn new(input: Box<dyn Input>) -> Self {
-        SimpleTestcase {
+    /// Create a new DefaultTestcase instace given an input
+    pub fn new(input: Box<InputT>) -> Self {
+        Testcase {
             input: Some(input),
             filename: None,
             metadatas: HashMap::default(),
         }
     }
+
+    /// Create a new DefaultTestcase instace given an input and a filename
+    pub fn new_with_filename(input: Box<InputT>, filename: &PathBuf) -> Self {
+        Testcase {
+            input: Some(input),
+            filename: filename,
+            metadatas: HashMap::default(),
+        }
+    }
 }
diff --git a/src/mutators/mod.rs b/src/mutators/mod.rs
index 8887039322..f045fa1299 100644
--- a/src/mutators/mod.rs
+++ b/src/mutators/mod.rs
@@ -1,21 +1,20 @@
 use crate::inputs::Input;
-use crate::utils::Rand;
+use crate::utils::{Rand, HasRand};
 use crate::corpus::Corpus;
 use crate::AflError;
 
 pub mod scheduled;
-pub use scheduled::ScheduledMutator;
-
-pub trait Mutator<InputT : Input> {
-
-    fn rand(&mut self) -> &mut Box<dyn Rand>;
+pub use scheduled::{ComposedByMutations, ScheduledMutator, HavocBytesMutator};
 
+pub trait Mutator<InputT : Input, RandT: Rand> : HasRand<RandT> {
+    /// Mutate a given input
     fn mutate(&mut self, input: &mut InputT, stage_idx: i32) -> Result<(), AflError>;
 
+    /// Post-process given the outcome of the execution
     fn post_exec(&mut self, _is_interesting: bool, _stage_idx: i32) -> Result<(), AflError> {
         Ok(())
     }
 
-    fn corpus(&mut self) -> &mut Option<Box<dyn Corpus>>;
-
+    /// Get the associated corpus, if any
+    fn corpus(&mut self) -> &mut Option<Box<dyn Corpus<InputT, RandT>>>;
 }
diff --git a/src/mutators/scheduled.rs b/src/mutators/scheduled.rs
index a474512122..cd26df644c 100644
--- a/src/mutators/scheduled.rs
+++ b/src/mutators/scheduled.rs
@@ -1,5 +1,5 @@
 use crate::mutators::Mutator;
-use crate::utils::Rand;
+use crate::utils::{Rand, HasRand};
 use crate::corpus::Corpus;
 use crate::inputs::{Input, HasBytesVec};
 use crate::AflError;
@@ -20,10 +20,10 @@ pub trait ComposedByMutations<InputT : Input> {
     fn add_mutation(&mut self, mutation: MutationFunction<Self, InputT>);
 }
 
-pub trait ScheduledMutator<InputT : Input>: Mutator<InputT> + ComposedByMutations<InputT> {
+pub trait ScheduledMutator<InputT : Input, RandT: Rand>: Mutator<InputT, RandT> + ComposedByMutations<InputT> {
     /// Computer the number of iterations used to apply stacked mutations
     fn iterations(&mut self, _input: &InputT) -> u64 {
-        1 << (1 + self.rand().below(7))
+        1 << (1 + self.rand_mut().below(7))
     }
 
     /// Get the next mutation to apply
@@ -34,7 +34,7 @@ pub trait ScheduledMutator<InputT : Input>: Mutator<InputT> + ComposedByMutation
         }
         let idx;
         {
-            idx = self.rand().below(count) as usize;
+            idx = self.rand_mut().below(count) as usize;
         }
         self.mutation_by_idx(idx)
     }
@@ -50,13 +50,22 @@ pub trait ScheduledMutator<InputT : Input>: Mutator<InputT> + ComposedByMutation
     }
 }
 
-pub struct DefaultScheduledMutator<InputT : Input> {
-    rand: Box<dyn Rand>,
-    corpus: Option<Box<dyn Corpus>>,
+pub struct DefaultScheduledMutator<InputT : Input, RandT: Rand> {
+    rand: Box<RandT>,
+    corpus: Option<Box<dyn Corpus<InputT, RandT>>>,
     mutations: Vec<MutationFunction<Self, InputT>>
 }
 
-impl<InputT : Input> ComposedByMutations<InputT> for DefaultScheduledMutator<InputT> {
+impl<InputT : Input, RandT: Rand> HasRand<RandT> for DefaultScheduledMutator<InputT, RandT> {
+    fn rand(&self) -> &Box<dyn Rand> {
+        &self.rand
+    }
+    fn rand_mut(&mut self) -> &mut Box<dyn Rand> {
+        &mut self.rand
+    }
+}
+
+impl<InputT : Input, RandT: Rand> ComposedByMutations<InputT> for DefaultScheduledMutator<InputT, RandT> {
     fn mutation_by_idx(&self, index: usize) -> Result<MutationFunction<Self, InputT>, AflError> {
         if index >= self.mutations.len() {
             return Err(AflError::Unknown("oob".to_string()));
@@ -73,15 +82,11 @@ impl<InputT : Input> ComposedByMutations<InputT> for DefaultScheduledMutator<Inp
     }
 }
 
-impl<InputT : Input> ScheduledMutator<InputT> for DefaultScheduledMutator<InputT> {
+impl<InputT : Input, RandT: Rand> ScheduledMutator<InputT> for DefaultScheduledMutator<InputT, RandT> {
     // Just use the default methods
 }
 
-impl<InputT : Input> Mutator<InputT> for DefaultScheduledMutator<InputT> {
-    fn rand(&mut self) -> &mut Box<dyn Rand> {
-        &mut self.rand
-    }
-
+impl<InputT : Input, RandT: Rand> Mutator<InputT, RandT> for DefaultScheduledMutator<InputT, RandT> {
     fn mutate(&mut self, input: &mut InputT, _stage_idx: i32) -> Result<(), AflError> {
         self.scheduled_mutate(input, _stage_idx)
     }
@@ -91,9 +96,9 @@ impl<InputT : Input> Mutator<InputT> for DefaultScheduledMutator<InputT> {
     }
 }
 
-impl<InputT : Input> DefaultScheduledMutator<InputT> {
+impl<InputT : Input, RandT: Rand> DefaultScheduledMutator<InputT> {
     /// Create a new DefaultScheduledMutator instance without mutations and corpus
-    pub fn new(rand: Box<dyn Rand>) -> Self {
+    pub fn new(rand: Box<RandT>) -> Self {
         DefaultScheduledMutator {
             rand: rand,
             corpus: None,
@@ -102,7 +107,7 @@ impl<InputT : Input> DefaultScheduledMutator<InputT> {
     }
 
     /// Create a new DefaultScheduledMutator instance specifying mutations and corpus too
-    pub fn new_all(rand: Box<dyn Rand>, corpus: Option<Box<dyn Corpus>>, mutations: Vec<MutationFunction<Self, InputT>>) -> Self {
+    pub fn new_all(rand: Box<RandT>, corpus: Option<Box<dyn Corpus>>, mutations: Vec<MutationFunction<Self, InputT>>) -> Self {
         DefaultScheduledMutator {
             rand: rand,
             corpus: corpus,
@@ -112,23 +117,19 @@ impl<InputT : Input> DefaultScheduledMutator<InputT> {
 }
 
 /// Bitflip mutation for inputs with a bytes vector
-pub fn mutation_bitflip<MutatorT: Mutator<InputT>, InputT: Input + HasBytesVec>(mutator: &mut MutatorT, input: &mut InputT) -> Result<(), AflError> {
-    let bit = mutator.rand().below(input.bytes().len() as u64) as usize;
+pub fn mutation_bitflip<MutatorT: Mutator<InputT, RandT>, InputT: Input + HasBytesVec, RandT: Rand>(mutator: &mut MutatorT, input: &mut InputT) -> Result<(), AflError> {
+    let bit = mutator.rand_mut().below(input.bytes().len() as u64) as usize;
     input.bytes_mut()[bit >> 3] ^= (128 >> (bit & 7)) as u8;
     Ok(())
 }
 
 /// Schedule some selected byte level mutations given a ScheduledMutator type
-pub struct HavocBytesMutator<ScheduledMutatorT: ScheduledMutator<InputT>, InputT: Input + HasBytesVec> {
+pub struct HavocBytesMutator<InputT: Input + HasBytesVec, RandT: Rand, ScheduledMutatorT: ScheduledMutator<InputT, RandT>> {
     scheduled: ScheduledMutatorT,
     _phantom: PhantomData<InputT>
 }
 
-impl<ScheduledMutatorT: ScheduledMutator<InputT>, InputT: Input + HasBytesVec> Mutator<InputT> for HavocBytesMutator<ScheduledMutatorT, InputT> {
-    fn rand(&mut self) -> &mut Box<dyn Rand> {
-        self.scheduled.rand()
-    }
-
+impl<InputT: Input + HasBytesVec, RandT: Rand, ScheduledMutatorT: ScheduledMutator<InputT, RandT>> Mutator<InputT, RandT> for HavocBytesMutator<InputT, RandT, ScheduledMutatorT> {
     fn mutate(&mut self, input: &mut InputT, stage_idx: i32) -> Result<(), AflError> {
         self.scheduled.mutate(input, stage_idx)
     }
@@ -138,7 +139,16 @@ impl<ScheduledMutatorT: ScheduledMutator<InputT>, InputT: Input + HasBytesVec> M
     }
 }
 
-impl<ScheduledMutatorT: ScheduledMutator<InputT>, InputT: Input + HasBytesVec> HavocBytesMutator<ScheduledMutatorT, InputT> {
+impl<InputT: Input + HasBytesVec, RandT: Rand, ScheduledMutatorT: ScheduledMutator<InputT, RandT>> HasRand<RandT> for HavocBytesMutator<InputT, RandT, ScheduledMutatorT> {
+    fn rand(&self) -> &Box<dyn Rand> {
+        self.scheduled.rand()
+    }
+    fn rand_mut(&mut self) -> &mut Box<dyn Rand> {
+        self.scheduled.rand_mut()
+    }
+}
+
+impl<InputT: Input + HasBytesVec, RandT: Rand, ScheduledMutatorT: ScheduledMutator<InputT, RandT>> HavocBytesMutator<InputT, RandT, ScheduledMutatorT> {
     /// Create a new HavocBytesMutator instance given a ScheduledMutator to wrap
     pub fn new(mut scheduled: ScheduledMutatorT) -> Self {
         scheduled.add_mutation(mutation_bitflip);
@@ -149,9 +159,9 @@ impl<ScheduledMutatorT: ScheduledMutator<InputT>, InputT: Input + HasBytesVec> H
     }
 }
 
-impl<InputT: Input + HasBytesVec> HavocBytesMutator<DefaultScheduledMutator<InputT>, InputT> {
+impl<InputT: Input + HasBytesVec, RandT: Rand> HavocBytesMutator<InputT, RandT, DefaultScheduledMutator<InputT, RandT>> {
     /// Create a new HavocBytesMutator instance wrapping DefaultScheduledMutator
-    pub fn new_default(rand: Box<dyn Rand>) -> Self {
+    pub fn new_default(rand: Box<RandT>) -> Self {
         let mut scheduled = DefaultScheduledMutator::new(rand);
         scheduled.add_mutation(mutation_bitflip);
         HavocBytesMutator {
diff --git a/src/stages/mod.rs b/src/stages/mod.rs
index 08e8c61c9e..c4f3e4962d 100644
--- a/src/stages/mod.rs
+++ b/src/stages/mod.rs
@@ -3,5 +3,5 @@ use crate::inputs::Input;
 use crate::AflError;
 /// Stages
 pub trait Stage {
-    fn perform(&mut self, input: &dyn Input, entry: &mut dyn Testcase) -> Result<(), AflError>;
+    fn perform(&mut self, input: &dyn Input, entry: &mut Testcase) -> Result<(), AflError>;
 }
diff --git a/src/utils.rs b/src/utils.rs
index e53e4fd51e..ed4e927d21 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -39,6 +39,15 @@ pub trait Rand: Debug {
     }
 }
 
+/// Has a Rand box field
+pub trait HasRand<RandT: Rand> {
+    /// Get the hold Rand instance
+    fn rand(&self) -> &Box<RandT>;
+
+    /// Get the hold Rand instance (mutable)
+    fn rand_mut(&mut self) -> &mut Box<RandT>;
+}
+
 const HASH_CONST: u64 = 0xa5b35705;
 
 /// XXH3 Based, hopefully speedy, rnd implementation