Add cast_list snippet

snippets/cast_list.md

@@ -0,0 +1,18 @@
+---
+title: cast_list
+tags: utility,list,beginner
+---
+
+Casts the provided value as an array if it's not one.
+
+Use `isinstance()` to check if the given value is a list and return it as-is or encapsulated in a list accordingly.
+
+```py
+def cast_list(val):
+  return val if isinstance(val, list) else [val]
+```
+
+```py
+cast_list('foo'); # ['foo']
+cast_list([1]); # [1]
+```