From b05aff67d68980135fee53ad9a280fbd2ad2e480 Mon Sep 17 00:00:00 2001
From: Iulian Dragos <jaguarul@gmail.com>
Date: Tue, 16 Sep 2025 11:58:43 +0200
Subject: [PATCH] Narrow the return type of a few implicits

This came up when upgrading our code base from an older vesion of mainargs, where we relied on chaining TokenReaders for Map and Seq. The implicit conversions require `TokensReader.Simple` as argument, but return the superclass `TokensReader`, which makes chaining impossible. Since the implementation is actually using the narrow type, we just expose it in the implicit def signature to make chaining work again.
---
 mainargs/src/TokensReader.scala | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mainargs/src/TokensReader.scala b/mainargs/src/TokensReader.scala
index 560a815..b3d4dc5 100644
--- a/mainargs/src/TokensReader.scala
+++ b/mainargs/src/TokensReader.scala
@@ -157,7 +157,7 @@ object TokensReader {
     def shortName = wrapped.shortName
   }
 
-  implicit def OptionRead[T: TokensReader.Simple]: TokensReader[Option[T]] = new OptionRead[T]
+  implicit def OptionRead[T: TokensReader.Simple]: TokensReader.Simple[Option[T]] = new OptionRead[T]
   class OptionRead[T: TokensReader.Simple] extends Simple[Option[T]] {
     def shortName = implicitly[TokensReader.Simple[T]].shortName
     def read(strs: Seq[String]) = {
@@ -174,7 +174,7 @@ object TokensReader {
 
   implicit def SeqRead[C[_] <: Iterable[_], T: TokensReader.Simple](implicit
       factory: Factory[T, C[T]]
-  ): TokensReader[C[T]] =
+  ): TokensReader.Simple[C[T]] =
     new SeqRead[C, T]
 
   class SeqRead[C[_] <: Iterable[_], T: TokensReader.Simple](implicit factory: Factory[T, C[T]])
@@ -198,7 +198,7 @@ object TokensReader {
     override def allowEmpty = true
   }
 
-  implicit def MapRead[K: TokensReader.Simple, V: TokensReader.Simple]: TokensReader[Map[K, V]] =
+  implicit def MapRead[K: TokensReader.Simple, V: TokensReader.Simple]: TokensReader.Simple[Map[K, V]] =
     new MapRead[K, V]
   class MapRead[K: TokensReader.Simple, V: TokensReader.Simple] extends Simple[Map[K, V]] {
     def shortName = "k=v"