Add KeyCanExtend and MapCanExtend marker traits

Signed-off-by: trivernis <trivernis@protonmail.com>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "trait-bound-typemap"
-version = "0.3.1"
+version = "0.3.2"
 edition = "2021"
 license = "Apache-2.0"
 readme = "README.md"

src/macros.rs

@@ -70,7 +70,9 @@ macro_rules! impl_typemap {
             }
         }
 
-        impl<T: $crate::MapKey<Map = M>, M: 'static $(+ $trt )+> FromIterator<$crate::TypeMapEntry<T>> for $map {
+        impl<T: $crate::TypeMap $(+ $trt )+> $crate::MapCanExtend<$map> for T {}
+
+        impl<T: $crate::KeyCanExtend<$map>> FromIterator<$crate::TypeMapEntry<T>> for $map {
             fn from_iter<T2: IntoIterator<Item = $crate::TypeMapEntry<T>>>(iter: T2) -> Self {
                 let map = iter
                     .into_iter()
@@ -81,7 +83,7 @@ macro_rules! impl_typemap {
             }
         }
 
-        impl<K: $crate::MapKey<Map = M>, M: 'static $(+ $trt )+> Extend<$crate::TypeMapEntry<K>> for $map {
+        impl<K: $crate::KeyCanExtend<$map>> Extend<$crate::TypeMapEntry<K>> for $map {
             fn extend<T: IntoIterator<Item = $crate::TypeMapEntry<K>>>(&mut self, iter: T) {
                 let iter = iter
                     .into_iter()

src/typemap_trait.rs

@@ -30,7 +30,7 @@ pub trait MapKey {
 /// A trait implemented by all typemaps that provides
 /// all basic typemap functions
 pub trait TypeMap {
-    type Key;
+    type Key: MapKey<Map = Self>;
 
     /// Creates a new typemap
     fn new() -> Self;
@@ -50,3 +50,13 @@ pub trait TypeMap {
     /// Returns if the map contains a given key
     fn contains_key<T: TypedKeyTrait<Self::Key>>(&self) -> bool;
 }
+
+/// Marker trait to signify that a given map can extend a different map (M)
+/// or construct it
+pub trait MapCanExtend<M> {}
+
+/// Marker trait to signify that the given key associated with a map can extend
+/// or construct a given map (M)
+pub trait KeyCanExtend<M> {}
+
+impl<T: MapKey<Map = M>, M: MapCanExtend<M2>, M2> KeyCanExtend<M2> for T {}