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--- language:impl [2022/05/13 08:40]
rajit
+++ language:impl [2023/04/09 18:06] (current)
rajit [Overrides]
@@ Line 245: / Line 245: @@
 representation of the Boolean variable.
+=== Overriding conditional instances and templated types ===
+An instance created in a type definition may be created only under certain circumstances.
+This can occur in templated types, where template parameters can affect the instances within the type.
+The override block has the simple syntax shown above. However, to account for conditional instances,
+the override block directives implicitly check if the instance exists before applying the override. (Note that
+ACT does not permit different types for the same instance name under different conditions.)
+When a type is being overridden by another, the new implementation may have additional template parameters.
+The override syntax above requires the complete list of template parameters to be specified. Instead, we also
+provide a single extension override syntax
+<code act>
++{
+    type<param1,param2,...,paramN>+ id;   // single ID only
+    ...
+ }
+</code>
+The ''+'' indicates that these are //extra// template parameter(s) that should be added to the existing ones that have already been specified for the instance ''id'' in the original type definition.