X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/caa6f4b99a79f95d15a6cc1e5b8dd27ea48b4d03..d1b394fa5cde326c2635997ddb7cda27a52d537d:/doc/concepts.tex

diff --git a/doc/concepts.tex b/doc/concepts.tex
index 8067739..b48746e 100644
--- a/doc/concepts.tex
+++ b/doc/concepts.tex
@@ -214,13 +214,13 @@ qualified by the defining class's nickname.
 \subsubsection{Slot initializers}
 As well as defining slot names and types, a class can also associate an
 \emph{initial value} with each slot defined by itself or one of its
-subclasses.  A class $C$ provides an \emph{initialization function} (see
+subclasses.  A class $C$ provides an \emph{initialization message} (see
 \xref{sec:concepts.lifecycle.birth}, and \xref{sec:structures.root.sodclass})
-which sets the slots of a \emph{direct} instance of the class to the correct
-initial values.  If several of $C$'s superclasses define initializers for the
-same slot then the initializer from the most specific such class is used.  If
-none of $C$'s superclasses define an initializer for some slot then that slot
-will be left uninitialized.
+whose methods set the slots of a \emph{direct} instance of the class to the
+correct initial values.  If several of $C$'s superclasses define initializers
+for the same slot then the initializer from the most specific such class is
+used.  If none of $C$'s superclasses define an initializer for some slot then
+that slot will be left uninitialized.
 
 The initializer for a slot with scalar type may be any C expression.  The
 initializer for a slot with aggregate type must contain only constant
@@ -270,7 +270,7 @@ slots.  If you want to hide implementation details, the best approach is to
 stash them in a dynamically allocated private structure, and leave a pointer
 to it in a slot.  (This will also help preserve binary compatibility, because
 the private structure can grow more members as needed.  See
-\xref{sec:fixme.compatibility} for more details.
+\xref{sec:fixme.compatibility} for more details.)
 
 \subsubsection{Vtables}
 
@@ -291,8 +291,8 @@ doesn't define any messages, so it doesn't have any methods.  In Sod, a class
 slot containing a function pointer is not at all the same thing as a method.)
 
 \subsubsection{Conversions}
-Suppose one has a value of type pointer to class type of some class~$C$, and
-wants to convert it to a pointer to class type of some other class~$B$.
+Suppose one has a value of type pointer-to-class-type for some class~$C$, and
+wants to convert it to a pointer-to-class-type for some other class~$B$.
 There are three main cases to distinguish.
 \begin{itemize}
 \item If $B$ is a superclass of~$C$, in the same chain, then the conversion
@@ -308,13 +308,13 @@ There are three main cases to distinguish.
   pointer.  The conversion can be performed using the appropriate generated
   upcast macro (see below); the general case is handled by the macro
   \descref{SOD_XCHAIN}{mac}.
-\item If $B$ is a subclass of~$C$ then the conversion is an \emph{upcast};
+\item If $B$ is a subclass of~$C$ then the conversion is a \emph{downcast};
   otherwise the conversion is a~\emph{cross-cast}.  In either case, the
   conversion can fail: the object in question might not be an instance of~$B$
-  at all.  The macro \descref{SOD_CONVERT}{mac} and the function
+  after all.  The macro \descref{SOD_CONVERT}{mac} and the function
   \descref{sod_convert}{fun} perform general conversions.  They return a null
   pointer if the conversion fails.  (There are therefore your analogue to the
-  \Cplusplus @|dynamic_cast<>| operator.)
+  \Cplusplus\ @|dynamic_cast<>| operator.)
 \end{itemize}
 The Sod translator generates macros for performing both in-chain and
 cross-chain upcasts.  For each class~$C$, and each proper superclass~$B$
@@ -741,7 +741,11 @@ environment in which it operates.
 
 Details of initialization are necessarily class-specific, but typically it
 involves setting the instance's slots to appropriate values, and possibly
-linking it into some larger data structure to keep track of it.
+linking it into some larger data structure to keep track of it.  It is
+possible for initialization methods to attempt to allocate resources, but
+this must be done carefully: there is currently no way to report an error
+from object initialization, so the object must be marked as incompletely
+initialized, and left in a state where it will be safe to tear down later.
 
 Initialization is performed by sending the imprinted instance an @|init|
 message, defined by the @|SodObject| class.  This message uses a nonstandard
@@ -840,9 +844,9 @@ allocated from the standard @|malloc| heap is done using the
 \descref{sod_destroy}[function]{fun}.
 
 \subsubsection{Teardown}
-Details of initialization are necessarily class-specific, but typically it
-involves setting the instance's slots to appropriate values, and possibly
-linking it into some larger data structure to keep track of it.
+Details of teardown are necessarily class-specific, but typically it
+involves releasing resources held by the instance, and disentangling it from
+any data structures it might be linked into.
 
 Teardown is performed by sending the instance the @|teardown| message,
 defined by the @|SodObject| class.  The message returns an integer, used as a
@@ -856,7 +860,7 @@ This simple protocol can be used, for example, to implement a reference
 counting system, as follows.
 \begin{prog}
   [nick = ref]                                                  \\
-  class ReferenceCountedObject \{                               \\ \ind
+  class ReferenceCountedObject: SodObject \{                    \\ \ind
     unsigned nref = 1;                                          \\-
     void inc() \{ me@->ref.nref++; \}                           \\-
     [role = around]                                             \\
