X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/8263521d93a9cdb7c64a7fcb79a9dd8bc6684d8a..c6b4ed992d81518f240509e6ab212d8fe705485a:/lib/sod-structs.3

diff --git a/lib/sod-structs.3 b/lib/sod-structs.3
index 16daa87..161fc4e 100644
--- a/lib/sod-structs.3
+++ b/lib/sod-structs.3
@@ -542,7 +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
@@ -626,13 +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
@@ -664,6 +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
@@ -688,7 +692,7 @@ will have
 .I different
 structures.
 .PP
-The instance layout split neatly into disjoint chains.
+The instance layout splits neatly into disjoint chains.
 This is necessary because
 each
 .B ichain
@@ -701,7 +705,7 @@ it doesn't matter that there are
 multiple method entry pointers
 for the same effective method
 as long as they all work correctly.
-Indeed, it's essential that they do,
+Indeed, it's essential that there are multiple entry pointers,
 because each chain's method entry function
 will need to apply a different offset to the receiver pointer
 before invoking the effective method.
@@ -865,8 +869,9 @@ be the most specific superclass of
 .I M
 in the same chain as
 .IR J .
-Then, if there is currently no class pointer of type
-.IR Q ,
+If there is currently no class pointer
+for the chain headed by
+.IR J ,
 then add a member
 .RS
 .IP
@@ -879,7 +884,13 @@ pointing to the appropriate
 .B islots
 structure within
 .IR M 's
-class object.
+class object,
+where
+.I Q
+is the most specific superclass of
+.I M
+in the same chain as
+.IR J .
 .RE
 .hP \*o
 Examine the superclass chains of
@@ -1103,6 +1114,12 @@ Finally, the class object is defined as
 .B #define
 .IB C __class
 .BI (& C __classobj. j . r )
+.br
+.B #define
+.IB C __cls_ k
+.BI (& C __classobj. k . n )
+.br
+\&...
 .PP
 The exported symbol
 .IB C __classobj
@@ -1121,7 +1138,32 @@ is the root metaclass of
 i.e., the metaclass of the least specific superclass of
 .IR C ;
 usually this is
-.BR "const SodClass *" .
+.BR "const SodClass\ *" .
+For each chain of
+.IR C 's
+metaclass, a macro
+.IB C __cls_ k
+is defined, usable as a pointer of type
+.B const
+.IR N \ \c
+.BR * ,
+where
+.I K
+and
+.I N
+are the chain's head and tail classes
+(i.e., the least- and most-specific classes in the chain)
+respectively;
+this macro is
+.I omitted
+if
+.IR N "\ =\ " R ,
+i.e., in the common case where
+.IR C 's
+metaclass is precisely the root metaclass,
+since the existing
+.IB C __class
+macro is already sufficient.
 .
 .\"--------------------------------------------------------------------------
 .SH SEE ALSO