Allocate Vec capacity based on size hints during decoding (#293)

ethabi/src/decoder.rs

@@ -49,6 +49,8 @@ fn decode_impl(types: &[ParamType], data: &[u8], validate: bool) -> Result<(Vec<
 	}
 
 	let mut tokens = vec![];
+	tokens.try_reserve_exact(types.len()).map_err(|_| Error::InvalidData)?;
+
 	let mut offset = 0;
 
 	for param in types {
@@ -178,6 +180,7 @@ fn decode_param(param: &ParamType, data: &[u8], offset: usize, validate: bool) -
 			let tail = &data[tail_offset..];
 
 			let mut tokens = vec![];
+			tokens.try_reserve_exact(len).map_err(|_| Error::InvalidData)?;
 			let mut new_offset = 0;
 
 			for _ in 0..len {
@@ -204,6 +207,7 @@ fn decode_param(param: &ParamType, data: &[u8], offset: usize, validate: bool) -
 			};
 
 			let mut tokens = vec![];
+			tokens.try_reserve_exact(len).map_err(|_| Error::InvalidData)?;
 
 			for _ in 0..len {
 				let res = decode_param(t, tail, new_offset, validate)?;

ethabi/src/filter.rs

@@ -50,9 +50,10 @@ impl Serialize for TopicFilter {
 }
 
 /// Acceptable topic possibilities.
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, Default, PartialEq, Eq)]
 pub enum Topic<T> {
 	/// Match any.
+	#[default]
 	Any,
 	/// Match any of the hashes.
 	OneOf(Vec<T>),
@@ -82,12 +83,6 @@ impl<T> Topic<T> {
 	}
 }
 
-impl<T> Default for Topic<T> {
-	fn default() -> Self {
-		Topic::Any
-	}
-}
-
 impl<T> From<Option<T>> for Topic<T> {
 	fn from(o: Option<T>) -> Self {
 		match o {