[proposal] fix: type check issues on encod/decode arguments

src/context.ts

@@ -1,6 +1,9 @@
 /* eslint-disable @typescript-eslint/ban-types */
 
-export type SplitTypes<T, U> = U extends T ? U : Exclude<T, U>;
+export type SplitTypes<T, U> = U extends T
+    ? Exclude<T, U> extends never ? T : Exclude<T, U>
+    : T;
+
 export type SplitUndefined<T> = SplitTypes<T, undefined>;
 
 export type ContextOf<ContextType> = ContextType extends undefined

src/decode.ts

@@ -42,11 +42,11 @@ export const defaultDecodeOptions: DecodeOptions = {};
  *
  * This is a synchronous decoding function. See other variants for asynchronous decoding: `decodeAsync()`, `decodeStream()`, `decodeArrayStream()`.
  */
-export function decode<ContextType>(
+export function decode<ContextType = undefined>(
   buffer: ArrayLike<number> | ArrayBuffer,
   options: DecodeOptions<SplitUndefined<ContextType>> = defaultDecodeOptions as any,
 ): unknown {
-  const decoder = new Decoder<ContextType>(
+  const decoder = new Decoder(
     options.extensionCodec,
     (options as typeof options & { context: any }).context,
     options.maxStrLength,

src/decodeAsync.ts

@@ -9,7 +9,7 @@ export async function decodeAsync<ContextType>(
 ): Promise<unknown> {
   const stream = ensureAsyncIterabe(streamLike);
 
-  const decoder = new Decoder<ContextType>(
+  const decoder = new Decoder(
     options.extensionCodec,
     (options as typeof options & { context: any }).context,
     options.maxStrLength,
@@ -27,7 +27,7 @@ export function decodeArrayStream<ContextType>(
 ) {
   const stream = ensureAsyncIterabe(streamLike);
 
-  const decoder = new Decoder<ContextType>(
+  const decoder = new Decoder(
     options.extensionCodec,
     (options as typeof options & { context: any }).context,
     options.maxStrLength,
@@ -46,7 +46,7 @@ export function decodeStream<ContextType>(
 ) {
   const stream = ensureAsyncIterabe(streamLike);
 
-  const decoder = new Decoder<ContextType>(
+  const decoder = new Decoder(
     options.extensionCodec,
     (options as typeof options & { context: any }).context,
     options.maxStrLength,

src/encode.ts

@@ -43,11 +43,11 @@ const defaultEncodeOptions: EncodeOptions = {};
  *
  * The returned buffer is a slice of a larger `ArrayBuffer`, so you have to use its `#byteOffset` and `#byteLength` in order to convert it to another typed arrays including NodeJS `Buffer`.
  */
-export function encode<ContextType>(
+export function encode<ContextType = undefined>(
   value: unknown,
   options: EncodeOptions<SplitUndefined<ContextType>> = defaultEncodeOptions as any,
 ): Uint8Array {
-  const encoder = new Encoder<ContextType>(
+  const encoder = new Encoder(
     options.extensionCodec,
     (options as typeof options & { context: any }).context,
     options.maxDepth,