X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/sod/blobdiff_plain/e0808c472145fc81e52898bc9ac289e10c4f4f41..faf3eb58d676c3abbef538784e26ca398d339caf:/lib/sod-structs.3

diff --git a/lib/sod-structs.3 b/lib/sod-structs.3
index da12cc5..672fe59 100644
--- a/lib/sod-structs.3
+++ b/lib/sod-structs.3
@@ -10,18 +10,19 @@
 .\" This file is part of the Sensible Object Design, an object system for C.
 .\"
 .\" SOD is free software; you can redistribute it and/or modify
-.\" it under the terms of the GNU General Public License as published by
-.\" the Free Software Foundation; either version 2 of the License, or
-.\" (at your option) any later version.
+.\" it under the terms of the GNU Library General Public License as
+.\" published by the Free Software Foundation; either version 2 of the
+.\" License, or (at your option) any later version.
 .\"
 .\" SOD is distributed in the hope that it will be useful,
 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-.\" GNU General Public License for more details.
+.\" GNU Library General Public License for more details.
 .\"
-.\" You should have received a copy of the GNU General Public License
-.\" along with SOD; if not, write to the Free Software Foundation,
-.\" Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+.\" You should have received a copy of the GNU Library General Public
+.\" License along with SOD; if not, write to the Free
+.\" Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+.\" MA 02111-1307, USA.
 .
 .\" Highlight using terminal escapes, rather than overstriking.
 .\"\X'tty: sgr 1'
@@ -68,6 +69,11 @@ struct sod_vtable {
 struct SodObject__vt_obj {
 \h'2n'const SodClass *_class;
 \h'2n'size_t _base;
+\h'2n'struct SodObject__vtmsgs_obj {
+\h'4n'void (*init)(SodObject *\fIme\fB, ...);
+\h'4n'void (*init__v)(SodObject *\fIme\fB, va_list);
+\h'4n'int (*teardown)(SodObject *\fIme\fB);
+\h'2n'} obj;
 };
 
 struct SodObject__ilayout {
@@ -84,9 +90,14 @@ extern const struct SodClass__ilayout SodObject__classobj;
 struct SodClass__vt_obj {
 \h'2n'const SodClass *_class;
 \h'2n'size_t _base;
+\h'2n'struct SodClass__vtmsgs_obj {
+\h'4n'void (*init)(SodClass *\fIme\fB, ...);
+\h'4n'void (*init__v)(SodClass *\fIme\fB, va_list);
+\h'4n'int (*teardown)(SodClass *\fIme\fB);
+\h'2n'} obj;
 };
 
-struct SodObject__ilayout {
+struct SodClass__ilayout {
 \h'2n'union {
 \h'4n'struct SodClass__ichain_obj {
 \h'6n'const struct SodClass__vt_obj *_vt;
@@ -94,8 +105,8 @@ struct SodObject__ilayout {
 \h'8n'const char *name;
 \h'8n'const char *nick;
 \h'8n'size_t initsz;
+\h'8n'size_t align;
 \h'8n'void *(*imprint)(void *\fIp\fB);
-\h'8n'void *(*init)(void *\fIp\fB);
 \h'8n'size_t n_supers;
 \h'8n'const SodClass *const *supers;
 \h'8n'size_t n_cpl;
@@ -211,7 +222,7 @@ and not really to be recommended.
 .SS The SodObject class
 The
 .B SodObject
-class defines no slots or messages.
+class defines no slots.
 Because
 .B SodObject
 has no direct superclasses,
@@ -219,8 +230,7 @@ there is only one chain,
 and no inherited slots or messages,
 so the single chain contains only a vtable pointer.
 .PP
-Since there are no messages,
-and
+Since
 .B SodClass
 also has only one chain,
 the vtable contains only the standard class pointer and offset-to-base
@@ -231,6 +241,79 @@ In an actual instance of
 the class pointer contains the address of
 .B SodObject__class
 and the offset is zero.
+.PP
+The
+.B init
+message is used to initialize a newly allocated instance.
+.PP
+This message uses a custom method combination
+which works like the standard method combination
+except that default behaviour
+specific to the receiver's direct class
+is invoked if no primary or around method overrides.
+This default behaviour may be invoked multiple times
+if some method calls on its
+.B next_method
+function more than once.
+.PP
+This default behaviour is to initialize the instance's slots
+using the defined slot initializers,
+and execute the initialization fragments.
+Each slot is initialized
+using the most specific applicable initializer,
+if any.
+Slots without an initializer
+are left uninitialized.
+.PP
+Slots are initialized and initialization fragments executed together,
+a superclass at a time:
+first, the superclass's slots are initialized (if any);
+then the superclass's initialization fragments (if any) are executed,
+starting with the least specific superclass first.
+Slots and initialization fragments defined by the same class
+are processed in the order in which they appear in the class definition.
+.PP
+There are no standard keyword arguments;
+methods on subclasses are free to
+introduce their own in the usual way.
+.PP
+It is usual to provide complex initialization behaviour as
+.B after
+methods.
+This ensures that slots have been initialized as necessary
+before the method executes.
+.PP
+The
+.B teardown
+message is used to tear down an instance which is no longer required.
+.PP
+The message returns an integer flag.
+A zero value means that the instance is safe to deallocate.
+A nonzero value means that the instance should not be deallocated,
+and that it is safe for the caller to simply forget about it.
+This simple protocol may be used, for example,
+to implement a reference-counting system.
+.PP
+This message uses a custom method combination
+which works like the standard method combination
+except that default behaviour is invoked if
+no primary or around method overrides.
+This default behaviour is to execute
+each superclass's teardown fragments,
+most specific first,
+and then return zero to indicate
+that the object is ready for deallocation.
+Teardown fragments defined by the same class
+are processed in the order in which they appear
+in the class definition.
+.PP
+It is usual to provide complex teardown behaviour as
+.B before
+methods.
+Logic to decide whether to allow deallocation
+is usually implemented as
+.B around
+methods.
 .
 .SS The SodClass class
 The
@@ -252,6 +335,9 @@ A pointer to the class's nickname.
 .B size_t initsz;
 The size in bytes required to store an instance of the class.
 .TP
+.B size_t align;
+A sufficient alignment for the class's instance storage.
+.TP
 .BI "void *(*imprint)(void *" p );
 A pointer to a function:
 given a pointer
@@ -266,20 +352,6 @@ but the slots are left untouched.
 The function returns its argument
 .IR p .
 .TP
-.BI "void *(*init)(void *" p );
-A pointer to a function:
-given a pointer
-.I p
-to at least
-.I initsz
-bytes of appropriately aligned memory,
-initialize an instance of the class in it:
-all of the vtable and class pointers are initialized,
-as are slots for which initializers are defined.
-Other slots are left untouched.
-The function returns its argument
-.IR p .
-.TP
 .B size_t n_supers;
 The number of direct superclasses.
 (This is zero exactly in the case of
@@ -470,7 +542,7 @@ struct \fIC\fB__ilayout {
 \h'6n'} \fIc\fB;
 \h'4n'} \fIc\fB;
 \h'4n'\fR...\fB
-\h'4n'struct \fIH\fB__ichain_\fIh\fB \fIh\fB;
+\h'4n'struct \fIA\fB__ichain_\fIh\fB \fIa\fB;
 \h'2n'} \fIh\fB;
 \h'2n'union \fIB\fB__ichainu_\fIi\fB \fIi\fB;
 \h'2n'\fR...\fB
@@ -554,13 +626,9 @@ for each of
 superclasses
 .IR A
 in the same chain in some (unimportant) order.
-A `pointer to
-.IR C '
-is always assumed
-(and, indeed, defined in C's type system)
-to be a pointer to the
-.B struct
-.IB C __ichain_ h \fR.
+The (somewhat obtuse) purpose of this union is to
+engage the `common initial sequence' rule of
+C99 (clause 6.5.2.3).
 .PP
 The
 .B ichain
@@ -592,6 +660,14 @@ then the last member is
 .IB C __islots 
 .IB c ;
 .PP
+A `pointer to
+.IR C '
+is always assumed
+(and, indeed, defined in C's type system)
+to be a pointer to the
+.B struct
+.IB C __ichain_ h \fR.
+.PP
 Finally, the
 .B islots
 structure simply contains one member for each slot defined by
@@ -663,6 +739,12 @@ extern const union \fIC\fB__vtu_\fIh\fB \fIC\fB__vtable_\fIh\fB;
 .ft P
 .fi
 .PP
+In the following,
+let
+.I M
+be the metaclass of
+.IR C .
+.PP
 The outer layer is a
 .B union
 .IB C __vtu_ h
@@ -892,6 +974,27 @@ defined as
 .IB an , 
 .B ...);
 .PP
+or a standard message which takes keyword arguments,
+defined as
+.IP
+.I tr
+.IB m ( \c
+.I t1
+.IB a1 ,
+.RB ... ,
+.I tn
+.IB an ?\&
+.IR tn +1
+.IR kn +1
+.RB [ =
+.IR dn +1] \c
+.B ,
+.I tm
+.I km
+.RB [ =
+.IR dm ] \c
+);
+.PP
 two entry points are defined:
 the usual `main' entry point
 which accepts a variable number of
@@ -899,7 +1002,8 @@ arguments,
 and a `valist' entry point
 which accepts an argument of type
 .B va_list
-in place of the variable portion of the argument list.
+in place of the variable portion of the argument list
+or keywords.
 .IP
 .I tr
 .BI (* m )( \c
@@ -949,6 +1053,7 @@ somewhat less ugly.
 If
 .I m
 takes a variable number of arguments,
+or keyword arguments,
 the macro is more complicated
 and is only available in compilers advertising C99 support,
 but the effect is the same.