defi asset pair as slice

Signed-off-by: dzmitry-lahoda <dzmitry@lahoda.pro>

frame/composable-traits/src/defi.rs

@@ -61,8 +61,8 @@ impl<AssetId: PartialEq, Balance: PartialOrd + Zero + SafeArithmetic> Sell<Asset
 
 /// given `base`, how much `quote` needed for unit
 /// see [currency pair](https://www.investopedia.com/terms/c/currencypair.asp)
-/// Pair with base and quote considered valid as it allows to have mixer(money laundering) like
-/// behavior.
+/// Pair with same base and quote is considered valid as it allows to have mixer, money laundering
+/// like behavior.
 #[repr(C)]
 #[derive(Encode, Decode, TypeInfo, Debug, Clone, PartialEq)]
 pub struct CurrencyPair<AssetId> {
@@ -77,10 +77,23 @@ impl<AssetId: PartialEq> CurrencyPair<AssetId> {
 		Self { base, quote }
 	}
 
-	pub fn as_array(&self) -> &[AssetId; 2] {
-		// adding lifetimes explicitly considered by rust as not needed, so lifetime is proper for
-		// return array
-		unsafe { sp_std::mem::transmute(self) }
+	///```rust
+	/// let pair = composable_traits::defi::CurrencyPair::<u128>::new(13, 42);
+	/// let slice =  pair.as_slice();
+	/// assert_eq!(slice[0], pair.base);
+	/// assert_eq!(slice[1], pair.quote);
+	/// drop(pair);
+	/// // next line will fail to compile
+	/// // let _ = slice[0];
+	/// ```
+	pub fn as_slice(&self) -> &[AssetId] {
+		unsafe { sp_std::slice::from_raw_parts(self as *const Self as *const AssetId, 2) }
+	}
+}
+
+impl<AssetId: PartialEq> AsRef<[AssetId]> for CurrencyPair<AssetId> {
+	fn as_ref(&self) -> &[AssetId] {
+		self.as_slice()
 	}
 }