dynamic casting functions should be available in TypeInfo_Class

[dlangBugzillaToGithub]

Ketmar Dark reported this on 2015-12-09T07:17:45Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=15427

CC List

• Ketmar Dark

Description

it's sometimes useful to emulate dynamic casting in runtime having only TypeInfo_Class at hands. now one has to rely on undocumented (and unexported) `_d_dynamic_cast()` and friends, writing something like this:


// get druntime cast function
private extern(C) void* _d_dynamic_cast (Object o, ClassInfo c);

bool isCastable (Object O, TypeInfo_Class ti) {
  return (_d_dynamic_cast(o, ti) !is null);
}


it would be fine to introduce and use a documented API for that, like this:

ti.dynamicCast(O)
ti.isBaseOf(O)


i.e. we should add these methods to TypeInfo_Class. also, the same methods should be added to TypeInfo_Interface.

[dlangBugzillaToGithub]

ketmar commented on 2015-12-09T07:19:24Z

p.s. `ti.dynamicCast(O)` should still return `void*`. not a big deal, it's very internal API anyway.

[dlangBugzillaToGithub]

ketmar commented on 2015-12-09T08:01:13Z

sample patch:

diff --git a/src/object.d b/src/object.d
index 097fc5a..6eb9163 100644
--- a/src/object.d
+++ b/src/object.d
@@ -21,6 +21,8 @@ private
 {
     extern (C) Object _d_newclass(const TypeInfo_Class ci);
     extern (C) void rt_finalize(void *data, bool det=true);
+    extern (C) void* _d_dynamic_cast(Object o, ClassInfo c);
+    extern (C) int _d_isbaseof(ClassInfo oc, ClassInfo c);
 }
 
 // NOTE: For some reason, this declaration method doesn't work
@@ -860,6 +862,17 @@ unittest
  */
 class TypeInfo_Class : TypeInfo
 {
+    final void* dynamicCast (Object o)
+    {
+        return (o !is null ? _d_dynamic_cast(o, this) : null);
+    }
+
+    // is this typeinfo base of `o`?
+    final bool baseOf (Object o)
+    {
+        return (o !is null ? (_d_isbaseof(typeid(o), this) != 0) : false);
+    }
+
     override string toString() const { return info.name; }
 
     override bool opEquals(Object o)