X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/1818107e8198734df843841a51bca3713bd37596..fa388683c9116be05ee1778150fd550fd2366a6e:/doc/structures.tex diff --git a/doc/structures.tex b/doc/structures.tex index 561075b..c8a0d9c 100644 --- a/doc/structures.tex +++ b/doc/structures.tex @@ -32,8 +32,8 @@ works very differently from the standard @|SodObject| described here. The concrete types described in \xref{sec:structures.common} and \ref{sec:structures.root} are declared by the header file @||. -The definitions described in sections \ref{sec:structures.layout} are defined -in the header file generated by the containing module. +The definitions described in \xref{sec:structures.layout} are defined in the +header file generated by the containing module. %%%-------------------------------------------------------------------------- \section{Common instance structure} \label{sec:structures.common} @@ -46,8 +46,8 @@ Instance chains contain slots and vtable pointers, as described below. All instances have the basic structure of a @|struct sod_instance|. \begin{describe}[struct sod_instance]{type} - {struct sod_instance \{ \\ \ind - const struct sod_vtable *_vt; \- \\ + {struct sod_instance \{ \\ \ind + const struct sod_vtable *_vt; \-\\ \};} The basic structure of all instances. Members are as follows. @@ -58,9 +58,9 @@ instances have the basic structure of a @|struct sod_instance|. \end{describe} \begin{describe}[struct sod_vtable]{type} - {struct sod_vtable \{ \\ \ind - const SodClass *_class; \\ - size_t _base; \- \\ + {struct sod_vtable \{ \\ \ind + const SodClass *_class; \\ + size_t _base; \-\\ \};} A vtable contains static metadata needed for efficient conversions and @@ -87,73 +87,142 @@ metaclass, and @|SodClass| is a subclass of @|SodObject|. Extensions can define additional root classes, but this is tricky, and not really to be recommended. + \subsection{The SodObject class} \label{sec:structures.root.sodobject} \begin{figure}[tbp] \begin{tabular}{p{10pt}p{10pt}} - \begin{prog} - struct SodObject__ilayout \{ \\ \ind - union \{ \\ \ind - struct SodObject__ichain_obj \{ \\ \ind - const struct SodObject__vt_obj *_vt; \- \\ - \}; \- \\ - \} obj; \- \\ + \begin{nprog} + struct SodObject__ilayout \{ \\ \ind + union \{ \\ \ind + struct SodObject__ichain_obj \{ \\ \ind + const struct SodObject__vt_obj *_vt; \-\\ + \} obj; \-\\ + \} obj; \-\\ \}; - \end{prog} + \end{nprog} & - \begin{prog} - struct SodObject__vt_obj \{ \\ \ind - const SodClass *_class; \\ - size_t _base; \- \\ + \begin{nprog} + struct SodObject__vt_obj \{ \\ \ind + const SodClass *_class; \\ + size_t _base; \\ + struct SodObject__vtmsgs_obj \{ \\ \ind + void (*init)(SodObject *me, ...); \\ + void (*init__v)(SodObject *me, va_list); \\ + int (*teardown)(SodObject *me); \-\\ + \} obj; \-\\ \}; - \end{prog} \\ + \end{nprog} \\ \end{tabular} \caption{Instance and vtable layout of @|SodObject|} \label{fig:structures.root.sodobject} \end{figure} \begin{describe}[SodObject]{cls} - {[metaclass = SodClass, lisp_metaclass = sod_class] \\ - class SodObject \{ \}} + {[nick = obj, metaclass = SodClass, + lisp_metaclass = sod_class] \\ + class SodObject \{ \\ \ind + void init(?); + \}} - The @|SodObject| class defines no slots or messages. Because @|SodObject| - has no direct superclasses, there is only one chain, and no inherited - slots or messages, so the single chain contains only a vtable pointer. + The @|SodObject| class defines no slots. Because @|SodObject| has no + direct superclasses, there is only one chain, and no inherited slots or + messages, so the single chain contains only a vtable pointer. - Since there are no messages, and @|SodClass| also has only one chain, the - vtable contains only the standard class pointer and offset-to-base members. - In a direct instance of @|SodObject| (why would you want one?) the class - pointer contains the address of @|SodObject__class| and the offset is zero. + Since @|SodClass| also has only one chain, the vtable contains only the + standard class pointer and offset-to-base members. In a direct instance of + @|SodObject| (why would you want one?) the class pointer contains the + address of @|SodObject__class| and the offset is zero. The instance and vtable layout of @|SodObject| is shown in \xref{fig:structures.root.sodobject}. + + The following messages are defined. + + \begin{describe}[obj.init]{msg}{void init(?);} + Initialize a newly allocated instance. + + 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 @|next_method| function more than once. + + 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. + + 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. + + There are no standard keyword arguments; methods on subclasses are free + to introduce their own in the usual way. + + It is usual to provide complex initialization behaviour as @|after| + methods. This ensures that slots have been initialized as necessary + before the method executes. + + For more details on instance construction, see + \xref{sec:concepts.lifecycle.birth}. + \end{describe} + + \begin{describe}[obj.teardown]{msg}{int teardown();} + Teardown an instance which is no longer required. + + 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. + + 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. + + It is usual to provide complex teardown behaviour as @|before| methods. + Logic to decide whether to allow deallocation is usually implemented as + @|around| methods. + \end{describe} \end{describe} + \subsection{The SodClass class} \label{sec:structures.root.sodclass} \begin{describe}[SodClass]{cls} - {class SodClass : SodObject \{ \\ \ind - const char *name; \\ - const char *nick; \\ - size_t initsz; \\ - void *(*imprint)(void *@

); \\ - void *(*init)(void *@

); \\ - size_t n_supers; \\ - const SodClass *const *supers; \\ - size_t n_cpl; \\ - const SodClass *const *cpl; \\ - const SodClass *link; \\ - const SodClass *head; \\ - size_t level; \\ - size_t n_chains; \\ - const struct sod_chain *chains; \\ - size_t off_islots; \\ - size_t islotsz; \- \\ + {[nick = cls, link = SodObject] \\ + class SodClass : SodObject \{ \\ \ind + const char *name; \\ + const char *nick; \\ + size_t initsz; \\ + size_t align; \\ + void *(*imprint)(void *@

); \\ + size_t n_supers; \\ + const SodClass *const *supers; \\ + size_t n_cpl; \\ + const SodClass *const *cpl; \\ + const SodClass *link; \\ + const SodClass *head; \\ + size_t level; \\ + size_t n_chains; \\ + const struct sod_chain *chains; \\ + size_t off_islots; \\ + size_t islotsz; \-\\ \}} - The @|SodClass| class defines no messages, but there are a number of slots. - Its only direct superclass is @|SodObject| and so (like its superclass) its - vtable is trivial. + The @|SodClass| class defines no additional messages , but there are a + number of slots. Its only direct superclass is @|SodObject| and so (like + its superclass) its vtable is simple. The slots defined are as follows. \begin{description} \let\makelabel\code @@ -164,18 +233,14 @@ recommended. \item[initsz] The size in bytes required to store an instance of the class. + \item[align] A sufficient alignment for the class's instance storage. + \item[imprint] A pointer to a function: given a pointer @

to at least @ bytes of appropriately aligned memory, `imprint' this memory it so that it becomes a minimally functional instance of the class: all of the vtable and class pointers are properly initialized, but the slots are left untouched. The function returns its argument @

. - \item[init] A pointer to a function: given a pointer @

to at least - @ 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 @

. - \item[n_supers] The number of direct superclasses. (This is zero exactly in the case of @|SodObject|.) @@ -189,7 +254,7 @@ recommended. \item[cpl] A pointer to an array of pointers to class objects listing all of the class's superclasses, from most- to least-specific, starting with - the class itself, so $c@->@|cls|.@|cpl|[0] = c$ for all class objects + the class itself, so $@|$c$@->cls.cpl[0]| = c$ for all class objects $c$. \item[link] If the class is a chain head, then this is a null pointer; @@ -197,21 +262,20 @@ recommended. might or might not be a direct superclass). \item[head] A pointer to the least-specific class in this class's chain; so - $c@->@|cls|.@|head|@->@|cls|.@|link|$ is always null, and either - $c@->@|cls|.@|link|$ is null (in which case $c@->@|cls|.@|head| = c$) or - $c@->@|cls|.@|head| = c@->@|cls|.@|link|@->@|cls|.@|head|$. + @|$c$@->cls.head@->cls.link| is always null, and either @|$c$@->cls.link| + is null (in which case $@|$c$@->cls.head| = c$) or $@|$c$@->cls.head| = + @|$c$@->cls.link@->cls.head|$. \item[level] The number of less specific superclasses in this class's - chain. If $c@->@|cls|.@|link|$ is null then $c@->@|cls|.@|level|$ is - zero; otherwise $c@->@|cls|.@|level| = - c@->@|cls|.@|link|@->@|cls|.@|level| + 1$. + chain. If @|$c$@->cls.link| is null then @|$c$@->cls.level| is zero; + otherwise $@|$c$@->cls.level| = @|$c$@->cls.link@->cls.level| + 1$. \item[n_chains] The number of chains formed by the class's superclasses. \item[chains] A pointer to an array of @|struct sod_chain| structures (see below) describing the class's superclass chains, in decreasing order of specificity of their most specific classes. It is always the case that - $c@->@|cls|.@|chains|[0].@|classes|[c@->@|cls|.@|level|] = c$. + $@|$c$@->cls.chains[0].classes[$c$@->cls.level]| = c$. \item[off_islots] The offset of the class's @|islots| structure relative to its containing @|ichain| structure. The class doesn't define any slots @@ -226,41 +290,41 @@ recommended. \end{describe} \begin{describe}[struct sod_chain]{type} - {struct sod_chain \{ \\ \ind - size_t n_classes; \\ - const SodClass *const *classes; \\ - size_t off_ichain; \\ - const struct sod_vtable *vt; \\ - size_t ichainsz; \- \\ + {struct sod_chain \{ \\ \ind + size_t n_classes; \\ + const SodClass *const *classes; \\ + size_t off_ichain; \\ + const struct sod_vtable *vt; \\ + size_t ichainsz; \-\\ \};} - The @|struct sod_chain| structure describes an individual chain of - superclasses. It has the following members. - \begin{description} \let\makelabel\code + The @|struct sod_chain| structure describes an individual chain of + superclasses. It has the following members. + \begin{description} \let\makelabel\code - \item[n_classes] The number of classes in the chain. This is always at - least one. + \item[n_classes] The number of classes in the chain. This is always at + least one. - \item[classes] A pointer to an array of class pointers listing the classes - in the chain from least- to most-specific. So - $@[i]@->@|cls|.@|head| = @[0]$ for all $0 \le i < - @$, $@[0]@->@|cls|.@|link|$ is always null, and - $@[i]@->@|cls|.@|link| = @[i - 1]$ if $1 \le i < - @$. + \item[classes] A pointer to an array of class pointers listing the classes + in the chain from least- to most-specific. So + $@|@[$i$]@->cls.head| = @|@[0]|$ for all $0 \le i < + @$, @|@[0]@->cls.link| is always null, and + $@|@[$i$]@->cls.link| = @|@[$i - 1$]|$ if $1 \le i < + @$. - \item[off_ichain] The size of the @|ichain| structure for this chain. + \item[off_ichain] The size of the @|ichain| structure for this chain. - \item[vt] The vtable for this chain. (It is possible, therefore, to - partially duplicate the behaviour of the @ function by walking - the chain structure.\footnote{% - There isn't enough information readily available to fill in the class - pointers correctly.} % - The @ function is much faster, though.) + \item[vt] The vtable for this chain. (It is possible, therefore, to + partially duplicate the behaviour of the @ function by walking + the chain structure.\footnote{% + There isn't enough information readily available to fill in the class + pointers correctly.} % + The @ function is much faster, though.) - \item[ichainsz] The size of the @|ichain| structure for this chain. + \item[ichainsz] The size of the @|ichain| structure for this chain. - \end{description} - \end{describe} + \end{description} +\end{describe} %%%-------------------------------------------------------------------------- \section{Class and vtable layout} \label{sec:structures.layout} @@ -279,6 +343,7 @@ In the description that follows, uppercase letters vary over class names, while the corresponding lowercase letters indicate the class nicknames. Throughout, we consider a class $C$ (therefore with nickname $c$). + \subsection{Generic instance structure} \label{sec:structures.layout.instance} @@ -286,25 +351,25 @@ The entire state of an instance of $C$ is contained in a single structure of type @|struct $C$__ilayout|. \begin{prog} - struct $C$__ilayout \{ \\ \ind - union $C$__ichainu_$h$ \{ \\ \ind - struct $C$__ichain_$h$ \{ \\ \ind - const struct $C$__vt_$h$ *_vt; \\ - struct $H$__islots $h$; \\ - \quad$\vdots$ \\ - struct $C$__islots \{ \\ \ind - @_1 @_1; \\ - \quad$\vdots$ \\ - @_n @_n; \- \\ - \} $c$; \- \\ - \} $c$; \\ - struct $H$__ichain_$h$ $h$; \\ - \quad$\vdots$ \- \\ - \} $h$; \\ - union $B$__ichainu_$i$ $i$; \\ - \quad$\vdots$ \- \\ - \}; - \\[\bigskipamount] + struct $C$__ilayout \{ \\ \ind + union $C$__ichainu_$h$ \{ \\ \ind + struct $C$__ichain_$h$ \{ \\ \ind + const struct $C$__vt_$h$ *_vt; \\ + struct $H$__islots $h$; \\ + \quad$\vdots$ \\ + struct $C$__islots \{ \\ \ind + @_1 @_1; \\ + \quad$\vdots$ \\ + @_n @_n; \-\\ + \} $c$; \-\\ + \} $c$; \\ + struct $H$__ichain_$h$ $h$; \\ + \quad$\vdots$ \-\\ + \} $h$; \\ + union $B$__ichainu_$i$ $i$; \\ + \quad$\vdots$ \-\\ + \}; \\+ + typedef struct $C$__ichain_$h$ $C$; \end{prog} @@ -315,7 +380,7 @@ transitive closure of the `links to' relation.) Chains are identified by naming their least specific classes; the least specific class in a chain is called the \emph{chain head}. Suppose that the chain head of the chain containing $C$ itself is named $H$ (though keep in mind that it's possible -that .$H$ is in fact $C$ itself.) +that $H$ is in fact $C$ itself.) \subsubsection{The ilayout structure} The @|ilayout| structure contains one member for each of $C$'s superclass @@ -369,6 +434,7 @@ type system) to be a pointer to the @|struct $C$__ichain_$h$|. Finally, the @|islots| structure simply contains one member for each slot defined by $C$ in the order they appear in the class definition. + \subsection{Generic vtable structure} \label{sec:structures.layout.vtable} As described above, each @|ichain| structure of an instance's storage has a @@ -392,26 +458,28 @@ method. A vtable for a class $C$ with chain head $H$ has the following general structure. \begin{prog} - union $C$__vtu_$h$ \{ \\ \ind - struct $C$__vt_$h$ \{ \\ \ind - const $P$ *_class; \\ - size_t _base; \\ - \quad$\vdots$ \\ - const $Q$ *_cls_$j$; \\ - \quad$\vdots$ \\ - ptrdiff_t _off_$i$; \\ - \quad$\vdots$ \\ - struct $C$__vtmsgs_$a$ \{ \\ \ind - @ (*@)($C$ *, $\dots$); \\ - \quad$\vdots$ \- \\ - \} $a$; \\ - \quad$\vdots$ \- \\ - \} $c$; \- \\ - \}; - \\[\bigskipamount] + union $C$__vtu_$h$ \{ \\ \ind + struct $C$__vt_$h$ \{ \\ \ind + const $P$ *_class; \\ + size_t _base; \\ + \quad$\vdots$ \\ + const $Q$ *_cls_$j$; \\ + \quad$\vdots$ \\ + ptrdiff_t _off_$i$; \\ + \quad$\vdots$ \\ + struct $C$__vtmsgs_$a$ \{ \\ \ind + @ (*@)($C$ *, $\dots$); \\ + \quad$\vdots$ \-\\ + \} $a$; \\ + \quad$\vdots$ \-\\ + \} $c$; \-\\ + \}; \\+ + extern const union $C$__vtu_$h$ $C$__vtable_$h$; \end{prog} +In the following, let $M$ be the metaclass of $C$. + \subsubsection{The vtu union} The outer layer is a @|union $C$__vtu_$h$| containing a member \begin{prog} @@ -420,18 +488,11 @@ The outer layer is a @|union $C$__vtu_$h$| containing a member for each of $C$'s superclasses $A$ in the same chain, with $C$ itself listed first. -This is mostly an irrelevant detail, -whose purpose is to defend against malicious compilers: -pointers are always to one of the inner -@|vt| -structures. -It's important only because it's the outer -@|vtu| -union which is exported by name. -Specifically, for each chain of -$C$'s -superclasses -there is an external object +This is mostly an irrelevant detail, whose purpose is to defend against +malicious compilers: pointers are always to one of the inner @|vt| +structures. It's important only because it's the outer @|vtu| union which is +exported by name. Specifically, for each chain of $C$'s superclasses there is +an external object \begin{prog} const union $A$__vtu_$i$ $C$__vtable_$i$; \end{prog} @@ -522,18 +583,28 @@ defined as \begin{prog} @_0 $m$(@_1 @_1, $\ldots$, @_n @_n, \dots); \end{prog} +or a standard message which takes keyword arguments, defined as +\begin{prog} + @_0 $m$(\=@_1 @_1, + $\ldots$, + @_n @_n? \+\\ + @_{n+1} @_{n+1} @[= @_{n+1}@], + $\ldots$, + @_m @_m @[= @_m@]); +\end{prog} two entry points are defined: the usual `main' entry point which accepts a variable number of arguments, and a `valist' entry point which accepts an argument of type @|va_list| in place of the variable portion of the argument -list. +list or keywords. \begin{prog} @_0 $m$($C$ *me, @_1 @_1, $\ldots$, - @_n @_n, \dots); \\ + @_n @_n, \dots); \\ @_0 $m$__v($C$ *me, @_1 @_1, $\ldots$, @_n @_n, va_list sod__ap); \end{prog} -\subsection{Additional definitions} \label{sec:structures.additional} + +\subsection{Additional definitions} \label{sec:structures.layout.additional} In addition to the instance and vtable structures described above, the following definitions are made for each class $C$. @@ -545,10 +616,10 @@ For each message $m$ directly defined by $C$ there is a macro definition which makes sending the message $m$ to an instance of (any subclass of) $C$ somewhat less ugly. -If $m$ takes a variable number of arguments, the macro is more complicated -and is only available in compilers advertising C99 support, but the effect is -the same. For each variable-argument message, there is also an additional -macro for calling the `valist' entry point. +If $m$ 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. For each variable-argument message, +there is also an additional macro for calling the `valist' entry point. \begin{prog} \#define $C$_$m$__v(@, $\ldots$, @) @@->_vt@->$c$.$m$__v(@, $\ldots$, @) @@ -566,7 +637,7 @@ defined for the sake of completeness. Finally, the class object is defined as \begin{prog} - extern const struct $R$__ilayout $C$__classobj; \\ + extern const struct $R$__ilayout $C$__classobj; \\ \#define $C$__class (\&$C$__classobj.$j$.$r$) \end{prog} The exported symbol @|$C$__classobj| contains the entire class instance.