Differences

This shows you the differences between two versions of the page.

--- at:tutorial:appendix [2008/07/10 16:12] – * tvcutsem
+++ at:tutorial:appendix [2008/07/10 16:17] – added tvcutsem
@@ Line 464: / Line 464: @@
 ==== Dynamic Variables ====
+The module ''/.at.lang.dynvars'' provides support for defining and using 'Dynamic Variables'. Dynamic variables 'simulate' dynamically scoped variables and are often used to parameterize large parts of code. For example, the 'current output stream'. A dynamic variable has the advantage over a simple global variable that it can only be assigned a value for the extent of a block of code.
+A dynamic variable can be defined as follows:
+<code>
+def name := dynamicVariable: initialValue;
+</code>
+It can be read as follows:
+<code>
+?name or name.value
+</code>
+It can be assigned only within a limited dynamic scope, as follows:
+<code>
+with: name is: newval do: { code }
+// or
+name.is: newval in: { code }
+</code>
+When ''code'' terminates (either normally or via an exception), the dynamic variable is automatically reset to its previous value.
+By convention, we prefix the names of dynamic variables with a ''d'', e.g. ''dTimeoutPeriod''. This makes it easier to remember to access these variables by means of ''?'' or ''.value''.
+You can find more usage examples of dynamic variables in the unit test included in the file ''at/lang/dynvars.at''.
 ==== Ambient References ====