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docs: remove advanced ql topic about determining specific types

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(cherry picked from commit 3d90f6fe71)
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james
2020-02-10 14:57:03 +00:00
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docs/language/learn-ql/advanced/advanced-ql.rst
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@@ -11,5 +11,4 @@ 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:`Determining the most specific types of a variable <determining-specific-types-variables>`
- :doc:`Monotonic aggregates in QL <monotonic-aggregates>`

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docs/language/learn-ql/advanced/determining-specific-types-variables.rst
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@@ -1,28 +0,0 @@
Determining the most specific types of a variable
=================================================
It is sometimes useful to be able to determine what types an entity has -- especially when you are unfamiliar with the library used by a query. To help with this, there is a predicate called ``getAQlClass()``, which returns the most specific QL types of the entity that it is called on.
This can be useful when you are not sure of the most precise class of a value. Discovering a more precise class can allow you to cast to it and use predicates that are not available on the more general class.
Example
-------
If you were working with a Java database, you might use ``getAQlClass()`` on every ``Expr`` in a callable called ``c``:
**Java example**
.. code-block:: ql
import java
from Expr e, Callable c
where
c.getDeclaringType().hasQualifiedName("my.namespace.name", "MyClass")
and c.getName() = "c"
and e.getEnclosingCallable() = c
select e, e.getAQlClass()
The result of this query is a list of the most specific types of every ``Expr`` in that function. You will see multiple results for some expressions because that expression is represented by more than one type.
For example, ``StringLiteral``\ s like ``"Hello"`` in Java belong to both the ``StringLiteral`` class (a specialization of the ``Literal`` class) and the ``CompileTimeConstantExpr`` class. So any instances of ``StringLiteral``\ s in the results will produce more than one result, one for each of the classes to which they belong.