diff --git a/src/fot/decoder.rs b/src/fot/decoder.rs
index 8eb9b59..5ec8a33 100644
--- a/src/fot/decoder.rs
+++ b/src/fot/decoder.rs
@@ -3,6 +3,12 @@ use anyhow::Result;
 use std::str;
 
 pub trait Decoder: Sized {
+    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self>;
+    fn encode(&self) -> Result<Raw>;
+    fn get_enc_size(&self) -> usize;
+}
+
+pub trait DecoderOpt: Sized {
     type Opt<'o>;
     fn decode(raw: &Raw, offset: usize, size: usize, opt: Option<Self::Opt<'_>>) -> Result<Self>;
     fn encode(&self) -> Result<Raw>;
@@ -10,8 +16,7 @@ pub trait Decoder: Sized {
 }
 
 impl Decoder for String {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, size: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
         let str = &raw.mem[offset..];
         match str.iter().position(|&c| c == 0) {
             Some(pos) => Ok(str::from_utf8(&str[..pos])?.to_string()),
diff --git a/src/fot/esh.rs b/src/fot/esh.rs
index a3b60a4..e5c1cee 100644
--- a/src/fot/esh.rs
+++ b/src/fot/esh.rs
@@ -76,8 +76,7 @@ impl ESHValue {
 }
 
 impl Decoder for ESHValue {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let data_type = rd.read_u32()?;
         let data_size = rd.read_u32()?;
@@ -249,8 +248,7 @@ pub struct ESH {
 }
 
 impl Decoder for ESH {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let tag: Tag = rd.read(0)?;
 
diff --git a/src/fot/fstring.rs b/src/fot/fstring.rs
index 93b147a..439ba15 100644
--- a/src/fot/fstring.rs
+++ b/src/fot/fstring.rs
@@ -24,8 +24,7 @@ pub struct FString {
 }
 
 impl Decoder for FString {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
         let mut rdr = Cursor::new(&raw.mem[offset..]);
         let flen = rdr.read_u32::<LittleEndian>()? as usize;
         let len = flen & !(1 << 31);
diff --git a/src/fot/sgd.rs b/src/fot/sgd.rs
index dd0ae95..7f5526e 100644
--- a/src/fot/sgd.rs
+++ b/src/fot/sgd.rs
@@ -15,8 +15,7 @@ pub struct SGD {
 }
 
 impl Decoder for SGD {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let tag: Tag = rd.read(0)?;
         let unk1 = rd.read_bytes(0x48)?;
diff --git a/src/fot/ssg.rs b/src/fot/ssg.rs
index 5634e37..86186fe 100644
--- a/src/fot/ssg.rs
+++ b/src/fot/ssg.rs
@@ -11,8 +11,7 @@ pub struct SSG {
 }
 
 impl Decoder for SSG {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, _: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, _: usize) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let tag: Tag = rd.read(0)?;
         let unk1 = rd.read_bytes(0x14)?;
diff --git a/src/fot/stream.rs b/src/fot/stream.rs
index 365a9e7..b7e166d 100644
--- a/src/fot/stream.rs
+++ b/src/fot/stream.rs
@@ -1,4 +1,4 @@
-use super::decoder::Decoder;
+use super::decoder::{Decoder, DecoderOpt};
 use super::raw::Raw;
 use anyhow::anyhow;
 use anyhow::Result;
@@ -46,14 +46,14 @@ impl<'a> ReadStream<'a> {
 
     // read_opt - decode with optional paramters. required for complex structure
     // with different origins (save / entfile) like entities
-    pub fn read_opt<'o, T: Decoder>(&mut self, size: usize, opt: T::Opt<'o>) -> Result<T> {
+    pub fn read_opt<'o, T: DecoderOpt>(&mut self, size: usize, opt: T::Opt<'o>) -> Result<T> {
         let val = T::decode(&self.raw, self.offset(), size, Some(opt))?;
         self.skip(val.get_enc_size());
         Ok(val)
     }
 
     pub fn read<T: Decoder>(&mut self, size: usize) -> Result<T> {
-        let val = T::decode(&self.raw, self.offset(), size, None)?;
+        let val = T::decode(&self.raw, self.offset(), size)?;
         self.skip(val.get_enc_size());
         Ok(val)
     }
diff --git a/src/fot/tag.rs b/src/fot/tag.rs
index d964491..b21e66f 100644
--- a/src/fot/tag.rs
+++ b/src/fot/tag.rs
@@ -10,8 +10,7 @@ pub struct Tag {
 }
 
 impl Decoder for Tag {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, size: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
         let mut rd = ReadStream::new(raw, offset);
         let name: String = rd.read(0)?;
         let version: String = rd.read(0)?;
diff --git a/src/fot/world.rs b/src/fot/world.rs
index 9f74d8a..a5bff36 100644
--- a/src/fot/world.rs
+++ b/src/fot/world.rs
@@ -67,8 +67,7 @@ impl World {
 }
 
 impl Decoder for World {
-    type Opt<'o> = ();
-    fn decode(raw: &Raw, offset: usize, size: usize, _: Option<()>) -> Result<Self> {
+    fn decode(raw: &Raw, offset: usize, size: usize) -> Result<Self> {
         let mut enc = ReadStream::new(raw, offset);
 
         let tag: Tag = enc.read(Self::WORLD_TAG_LEN)?;