source/blog/posts/2009/11/13-annotations--properties-and-safety-are-coming-to-d.rst

   1 Title: Annotations, properties and safety are coming to D
   2 Tags: en, d, annotation, property, safe, trusted
   3
   4 Two days ago, the documentation of functions were updated__ with some
   5 interesting revelations...
   6
   7 __ http://www.dsource.org/projects/phobos/changeset/1329
   8
   9 After **a lot** of discussion about properties needing improvements [*]_, it
  10 seems like they are now officially implemented using the *annotations*, which
  11 seems to be official too now, after some more discussion [*]_.
  12
  13 Annotations will be used for another longly discussed feature, a *safe* [*]_
  14 subset of the language. At first it was thought as some kind of separate
  15 language, activated through a flag ``-safe`` (which is already in the DMD
  16 compiler but has no effect AFAIK), but after the discussion it seems that it
  17 will be part of the main language, being able to *mark* parts of the code as
  18 ``safe`` or ``trusted`` (unmarked functions are ``unsafe``).
  19
  20 Please take a look at the discussions for the details but here are some
  21 examples:
  22
  23 Annotations
  24 -----------
  25
  26 They are prefixed with ``@`` and are similar to attributes__ (not class
  27 attributes; ``static``, ``final``, ``private``, etc. see the specs for
  28 details).
  29
  30 __ http://www.digitalmars.com/d/2.0/attribute.html
  31
  32 For example::
  33
  34     @ann1 {
  35         // things with annotation ann1
  36     }
  37
  38     @ann2 something; // one thing with annotation ann2
  39
  40     @ann3:
  41         // From now on, everything has the ann3 annotation
  42
  43 For now, only the compiler can define annotations, but maybe in the future the
  44 user can do it too and access to them using some reflection. Time will tell, as
  45 usual, Walter is completely silent about this.
  46
  47
  48 Properties
  49 ----------
  50
  51 Properties are now marked with the ``@property`` annotation (maybe a shorter
  52 annotation would be better? Like ``@prop``).  Here is an example::
  53
  54     class Foo {
  55         @property int bar() { ... } // read-only
  56         @property { // read-write
  57             char baz() { ... }
  58             void baz(char x) { ...}
  59         }
  60
  61
  62 Safe
  63 ----
  64
  65 Now functions can be marked with the annotations ``@safe`` or ``@trusted``.
  66 Unmarked functions are *unsafe*. Safe functions can only use a subset of the
  67 language that it's *safe* by some definition (*memory safe* and *no undefined
  68 behavior* are probably the most accepted definition). Here is a list of things
  69 a safe function can't do:
  70
  71 - No casting from a pointer type to any type other than ``void*``.
  72 - No casting from any non-pointer type to a pointer type.
  73 - No modification of pointer values.
  74 - Cannot access unions that have pointers or references overlapping with other types.
  75 - Calling any unsafe functions.
  76 - No catching of exceptions that are not derived from ``class Exception``.
  77 - No inline assembler.
  78 - No explicit casting of mutable objects to immutable.
  79 - No explicit casting of immutable objects to mutable.
  80 - No explicit casting of thread local objects to shared.
  81 - No explicit casting of shared objects to thread local.
  82 - No taking the address of a local variable or function parameter.
  83 - Cannot access ``__gshared`` variables.
  84
  85 There is some discussion about bound-checking being active in safe functions
  86 even when the ``-release`` compiler flag is used.
  87
  88 Trusted functions are not checked by the compiler, but trusted to be safe
  89 (should be manually verified by the writer of the function), and can use
  90 unsafe code and call unsafe functions.
  91
  92 .. [*] Here are *some* links to the property discussions:
  93
  94     - http://www.digitalmars.com/d/archives/digitalmars/D/property_keyword_96728.html
  95     - http://www.digitalmars.com/d/archives/digitalmars/D/resolveProperties_dmd_hacking_96677.html
  96     - http://www.digitalmars.com/d/archives/digitalmars/D/property_syntax_strawman_94692.html
  97     - http://www.digitalmars.com/d/archives/digitalmars/D/property_getProperty_setProperty_94599.html
  98     - http://www.digitalmars.com/d/archives/digitalmars/D/Property_and_method_groups_94505.html
  99     - http://www.digitalmars.com/d/archives/digitalmars/D/Yet_a_new_properties_proposal_94316.html
 100     - http://www.digitalmars.com/d/archives/digitalmars/D/Properties_problems_94264.html
 101     - http://www.digitalmars.com/d/archives/digitalmars/D/Properties_a.b.c_3_94225.html
 102     - http://www.digitalmars.com/d/archives/digitalmars/D/Properties\_--_another_one_that_gets_me_94223.html
 103     - http://www.digitalmars.com/d/archives/digitalmars/D/properties_using_template_mixins_and_alias_this_87952.html
 104     - http://www.digitalmars.com/d/archives/digitalmars/D/property_syntax_problems_83326.html
 105     - http://www.digitalmars.com/d/archives/digitalmars/D/DIP4_Properties_93698.html
 106     - http://www.digitalmars.com/d/archives/digitalmars/D/new_DIP5_Properties_2_93917.html
 107     - http://prowiki.org/wiki4d/wiki.cgi?DocComments/Property
 108
 109 .. [*] Discussion about annotations:
 110
 111     - http://www.digitalmars.com/d/archives/digitalmars/D/Idea_For_Attributes_Annotations_85768.html
 112     - http://www.digitalmars.com/d/archives/digitalmars/D/DIP6_Attributes_94648.html
 113
 114 .. [*] Discussions about SafeD:
 115
 116     - http://www.digitalmars.com/d/archives/digitalmars/D/SafeD_and_Nullable_concept_82152.html
 117     - http://www.digitalmars.com/d/archives/digitalmars/D/Memory_safety_C_D_and_more_89441.html
 118     - http://www.digitalmars.com/d/archives/digitalmars/D/safety_model_in_D_99989.html
 119     - http://www.digitalmars.com/d/archives/digitalmars/D/An_interesting_consequence_of_safety_requirements_100057.html
 120     - http://www.digitalmars.com/d/archives/digitalmars/D/Safety_undefined_behavior_safe_trusted_100138.html
 121
 122 .. vim: set et sw=4 sts=4 :