Constant instances (in particular: about canonical instances)

Author: eernstg

specification/dartLangSpec.tex

@@ -10428,6 +10428,13 @@ \subsubsection{Lists}
 the result of evaluating a constant expression.%
 }
 
+\LMHash{}%
+The canonical instance of a constant list literal has a type argument
+which is transitively alias expanded
+(\ref{typedef})
+and normalized
+(\ref{typeNormalization}).
+
 \LMHash{}%
 A run-time list literal
 \code{<$T$>[\List{\ell}{1}{m}]}
@@ -11242,6 +11249,13 @@ \subsubsection{Sets}
 the result of evaluating a constant expression.%
 }
 
+\LMHash{}%
+The canonical instance of a constant set literal has a type argument
+which is transitively alias expanded
+(\ref{typedef})
+and normalized
+(\ref{typeNormalization}).
+
 \LMHash{}%
 A run-time set literal \code{<$T$>\{\List{\ell}{1}{n}\}}
 is evaluated as follows:
@@ -11437,6 +11451,13 @@ \subsubsection{Maps}
 the result of evaluating a constant expression.%
 }
 
+\LMHash{}%
+The canonical instance of a constant map literal has type arguments
+which are transitively alias expanded
+(\ref{typedef})
+and normalized
+(\ref{typeNormalization}).
+
 \LMHash{}%
 A run-time map literal
 \code{<$T_1, T_2$>\{\List{\ell}{1}{m}\}}
@@ -12221,6 +12242,14 @@ \subsubsection{Const}
 The constructor need only be executed once per call site, at compile time.%
 }
 
+\LMHash{}%
+For instances of a generic class,
+the canonical instance of a constant object expression has type arguments
+which are transitively alias expanded
+(\ref{typedef})
+and normalized
+(\ref{typeNormalization}).
+
 \LMHash{}%
 It is a \Error{compile-time error} if evaluation of a constant object
 results in an uncaught exception being thrown.
@@ -13294,6 +13323,14 @@ \subsection{Function Closurization}
 are canonicalized.%
 }
 
+\LMHash{}%
+The canonical instance of a constant function closurization has
+parameter types and a return type
+which are transitively alias expanded
+(\ref{typedef})
+and normalized
+(\ref{typeNormalization}).
+
 
 \subsection{Generic Function Instantiation}
 \LMLabel{genericFunctionInstantiation}
@@ -24190,36 +24227,10 @@ \subsubsection{Null promotion}
 These are extended as per
 [separate proposal](https://github.com/dart-lang/language/blob/master/resources/type-system/flow-analysis.md).
 
-
 \paragraph{Constant instances}
 
 !!!TODO!!!
 
-Any two instances which are otherwise identical except for their
-generic type arguments shall be considered identical if those generic
-type arguments compare equal using the definition of runtime type
-object equality defined above.  That is, comparison (or
-canonicalization) of constant instances of generic classes is
-performed relative to the normal forms of their generic type
-arguments.  Hence, an instance of \code{$C$<$T_0$>} compares identical
-to \code{C<$T_1$>} if $T_0$ and $T_1$ have the same normal form (up to
-the identity of bound variables), and the objects are otherwise
-identical.
-
-Implementations of the Dart runtime semantics rely on canonicalization of
-constant objects to allow the identity semantics specified above to be
-implemented as fast pointer equality checks on the reference to the canonical
-form.  The definition above defines equivalence classes of constant objects for
-which we must choose the canonical representative.
-
-We define the choice of the canonical instance representing an
-equivalence class of constant objects as follows.
-
-All generic constant constructors and generic constant
-literals are evaluated using the type arguments provided, and canonicalization
-is performed with respect to the normal form of the type arguments.  This
-ensures a consistent semantics, since it is not observable which instance is
-chosen as the canonical representative.
 
 \subsubsection{Null check operator}