diff options
Diffstat (limited to 'doc/tut2.txt')
| -rw-r--r-- | doc/tut2.txt | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/doc/tut2.txt b/doc/tut2.txt index 4d30b1445..e1ac20074 100644 --- a/doc/tut2.txt +++ b/doc/tut2.txt @@ -56,12 +56,12 @@ Objects have access to their type at runtime. There is an .. code-block:: nim type - Person = object of RootObj + Person = ref object of RootObj name*: string # the * means that `name` is accessible from other modules age: int # no * means that the field is hidden from other modules - Student = object of Person # Student inherits from Person - id: int # with an id field + Student = ref object of Person # Student inherits from Person + id: int # with an id field var student: Student @@ -69,6 +69,7 @@ Objects have access to their type at runtime. There is an assert(student of Student) # is true # object construction: student = Student(name: "Anton", age: 5, id: 2) + echo student[] Object fields that should be visible from outside the defining module have to be marked by ``*``. In contrast to tuples, different object types are @@ -82,6 +83,9 @@ no ancestor are implicitly ``final``. You can use the ``inheritable`` pragma to introduce new object roots apart from ``system.RootObj``. (This is used in the GTK wrapper for instance.) +Ref objects should be used whenever inheritance is used. It isn't strictly +necessary, but with non-ref objects assignments such as ``let person: Person = +Student(id: 123)`` will truncate subclass fields. **Note**: Composition (*has-a* relation) is often preferable to inheritance (*is-a* relation) for simple code reuse. Since objects are value types in @@ -228,7 +232,7 @@ is needed: .. code-block:: nim type - Socket* = object of RootObj + Socket* = ref object of RootObj FHost: int # cannot be accessed from the outside of the module # the `F` prefix is a convention to avoid clashes since # the accessors are named `host` @@ -241,8 +245,8 @@ is needed: ## getter of hostAddr s.FHost - var - s: Socket + var s: Socket + new s s.host = 34 # same as `host=`(s, 34) (The example also shows ``inline`` procedures.) @@ -313,8 +317,8 @@ dispatching: .. code-block:: nim type - Thing = object of RootObj - Unit = object of Thing + Thing = ref object of RootObj + Unit = ref object of Thing x: int method collide(a, b: Thing) {.inline.} = @@ -326,8 +330,9 @@ dispatching: method collide(a: Unit, b: Thing) {.inline.} = echo "2" - var - a, b: Unit + var a, b: Unit + new a + new b collide(a, b) # output: 2 |