solution: conversion from trait type

src/path_custom.rs

@@ -67,6 +67,16 @@ impl TryFrom<&str> for CustomHDPath {
     }
 }
 
+impl std::convert::From<&dyn HDPath> for CustomHDPath {
+    fn from(value: &dyn HDPath) -> Self {
+        let mut path = Vec::with_capacity(value.len() as usize);
+        for i in 0..value.len() {
+            path.push(value.get(i).expect("no-path-element"));
+        }
+        CustomHDPath(path)
+    }
+}
+
 impl std::fmt::Display for CustomHDPath {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "m")?;
@@ -190,6 +200,7 @@ impl std::convert::From<&CustomHDPath> for DerivationPath {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::StandardHDPath;
 
     #[test]
     pub fn to_string() {
@@ -226,6 +237,15 @@ mod tests {
         assert_eq!(&PathValue::Normal(0), act.0.get(4).unwrap());
     }
 
+    #[test]
+    pub fn try_from_common_trait() {
+        let source = StandardHDPath::from_str("m/84'/0'/1'/2/3").unwrap();
+        let act = CustomHDPath::from(source.to_trait());
+        assert_eq!(
+            CustomHDPath::try_from("m/84'/0'/1'/2/3").unwrap(), act
+        );
+    }
+
     #[test]
     pub fn try_from_bignum() {
         let act = CustomHDPath::try_from("m/44'/12'/345'/6789/101112").unwrap();

src/traits.rs

@@ -1,5 +1,7 @@
 use crate::{PathValue, CustomHDPath};
 use byteorder::{BigEndian, WriteBytesExt};
+#[cfg(feature = "with-bitcoin")]
+use bitcoin::util::bip32::{ChildNumber, DerivationPath};
 
 /// General trait for an HDPath.
 /// Common implementations are [`StandardHDPath`], [`AccountHDPath`] and [`CustomHDPath`]
@@ -51,12 +53,29 @@ pub trait HDPath {
     }
 }
 
+#[cfg(feature = "with-bitcoin")]
+impl std::convert::From<&dyn HDPath> for DerivationPath {
+    fn from(value: &dyn HDPath) -> Self {
+        let mut path = Vec::with_capacity(value.len() as usize);
+        for i in 0..value.len() {
+            path.push(ChildNumber::from(value.get(i).expect("no-path-element")));
+        }
+        DerivationPath::from(path)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::{StandardHDPath, AccountHDPath};
     use std::str::FromStr;
 
+    impl StandardHDPath {
+        pub fn to_trait(&self) -> &dyn HDPath {
+            self
+        }
+    }
+
     #[test]
     fn get_parent_from_std() {
         let act = StandardHDPath::from_str("m/44'/0'/1'/1/2").unwrap();
@@ -100,4 +119,21 @@ mod tests {
             "m/84'/0'/1'/0", parent.to_string()
         );
     }
+}
+
+#[cfg(all(test, feature = "with-bitcoin"))]
+mod tests_with_bitcoin {
+    use crate::{StandardHDPath};
+    use std::str::FromStr;
+    use bitcoin::util::bip32::{DerivationPath};
+
+    #[test]
+    fn convert_to_bitcoin() {
+        let source = StandardHDPath::from_str("m/44'/0'/1'/1/2").unwrap();
+        let act = DerivationPath::from(source.to_trait());
+        assert_eq!(
+            DerivationPath::from_str("m/44'/0'/1'/1/2").unwrap(),
+            act
+        )
+    }
 }