docs: delete constraining-types.rst

(cherry picked from commit 142106bc99)

docs/language/learn-ql/advanced/advanced-ql.rst

@@ -10,5 +10,4 @@ Advanced QL
 
 Topics on advanced uses of QL. These topics assume that you are familiar with QL and the basics of query writing.
 
--  :doc:`Choosing appropriate ways to constrain types <constraining-types>`
 -  :doc:`Monotonic aggregates in QL <monotonic-aggregates>`

docs/language/learn-ql/advanced/constraining-types.rst

@@ -1,73 +0,0 @@
-Constraining types
-==================
-
-Type constraint methods
------------------------
-
-.. pull-quote::
-
-   Note
-
-   The examples below use the CodeQL library for Java. All libraries support using these methods to constrain variables, the only difference is in the names of the classes used.
-
-There are several ways of imposing type constraints on variables:
-
--  Use an ``instanceof`` test, for example:
-
-   .. code-block:: ql
-
-      import java
-
-      from Type t
-      where t instanceof Class
-      select t
-
--  Use a cast, for example:
-
-   .. code-block:: ql
-
-      import java
-
-      from Type t
-      where t.(Class).getASupertype().hasName("List")
-      select t
-
--  Set the variable equal to another variable with the required type using exists, for example:
-
-   .. code-block:: ql
-
-      import java
-
-      from Type t
-      where exists(Class c |
-          c = t
-          and c.getASupertype().hasName("List")
-      )
-      select t
-
--  Pass the variable to a predicate that expects a variable of the required type, for example:
-
-   .. code-block:: ql
-
-      import java
-
-      predicate derivedFromList(Class c) {
-          c.getASupertype().hasName("List")
-      }
-
-      from Type t
-      where derivedFromList(t)
-      select t
-
-All of these methods constrain the variable ``t`` to have values of type ``Class``.
-
-Choosing between the methods
-----------------------------
-
-These methods have advantages and disadvantages depending on the extent to which you need to work with the variable as the new type:
-
--  ``instanceof`` only checks that the variable has the required type.
--  A cast gives you one, and only one, access to the variable as the new type.
--  Creating a new variable with ``exists`` or a predicate parameter allows repeated access to the variable as the new type.
-
-   -  Note that due to the ability to overload predicates in a class, predicates that belong to a class must be supplied with arguments of the exact type they specify, and so this technique will not work in that situation.