metamodel: fix and comment upcast_for

[nit.git] / src / metamodel / static_type.nit

diff --git a/src/metamodel/static_type.nit b/src/metamodel/static_type.nit
index 0516f4f..25b41f8 100644 (file)
--- a/src/metamodel/static_type.nit
+++ b/src/metamodel/static_type.nit
@@ -325,6 +325,24 @@ abstract class MMType
 
        # Adapt self to another local class context
        # Useful for genericity
+       # 'c' Must be a super-class of self
+       # Example:
+       #   class A[E]
+       #   class B[F] special A[F]
+       #   class C[G] special B[String]
+       #   class D special C[Float]
+       # 'A[Int]'.upcast_for('A') -> 'A[Int]'
+       # 'A[Int]'.upcast_for('B') -> abort
+       # 'B[Int]'.upcast_for('B') -> 'B[Int]'
+       # 'B[Int]'.upcast_for('A') -> 'A[Int]'
+       # 'B[Int]'.upcast_for('C') -> abort
+       # 'C[Int]'.upcast_for('C') -> 'C[Int]'
+       # 'C[Int]'.upcast_for('B') -> 'B[String]'
+       # 'C[Int]'.upcast_for('A') -> 'A[String]'
+       # 'D'.upcast_for('D') -> 'D'
+       # 'D'.upcast_for('C') -> 'C[Float]'
+       # 'D'.upcast_for('B') -> 'C[String]'
+       # 'D'.upcast_for('A') -> 'A[String]'
        meth upcast_for(c: MMLocalClass): MMType is abstract
 
        # Return a type approximation if the reveiver is not self
@@ -390,11 +408,12 @@ end
 # The type of null
 class MMTypeNone
 special MMType
-       redef readable attr _module: MMModule
-       redef meth <(t) do return true
-       redef meth is_supertype(t) do return false
-       redef meth local_class do abort
-       redef meth upcast_for(c) do return self
+       redef readable attr _module: MMModule
+       redef meth <(t) do return true
+       redef meth to_s do return "null"
+       redef meth is_supertype(t) do return false
+       redef meth local_class do abort
+       redef meth upcast_for(c) do abort
 
        private init(m: MMModule) do _module = m
 end