struct :init :fini specifiers.

* share/txr/stdlib/struct.tl (defstruct): New (:init ...) and
(:fini ...) syntax can be used in the slot list to specify
an initialization function and a gc-finalization function.

* txr.1: Documented.

1 files changed, 58 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 02598449..b4bdacb4 100644
--- a/txr.1
+++ b/txr.1
@@ -17835,6 +17835,64 @@ Such functions are called using the
 syntax which doesn't insert the instance name into
 the argument list.
 
+.meIP (:init <> ( param ) << body-form *)
+The
+.code :init
+descriptor doesn't describe a slot. Rather, it specifies code
+which is executed when a structure is instantiated, after
+the slot initializations specific to the structure type
+are performed. The code consists of
+.metn body-form -s
+which are evaluated in order in a lexical scope in
+which the variable
+.meta param
+is bound to the structure object.
+
+The
+.code :init
+specifier may not appear more than once in a given
+.code defstruct
+form.
+
+When an object with one or more levels of inheritance
+is instantiated, the
+.code :init
+code of a base structure type, if any, is executed
+before any initializations specific to a derived
+structure type.
+
+Initializers in base structures must be careful about assumptions about slot
+kinds, because derived structures can alter static slots to instance slots or
+vice versa. To avoid an unwanted initialization being applied to the
+wrong kind of slot, initialization code can be made conditional on the
+outcome of
+.code static-slot-p
+applied to the slot.
+(Code generated by
+.code defstruct
+for initializing instance slots performs this kind of check).
+
+.meIP (:fini <> ( param ) << body-form *)
+The
+.code :fini
+descriptor doesn't describe a slot. Rather, it specifies
+a finalization function which is associated with the
+structure instance, as if by use of the
+.code finalize
+function. This finalization registration takes place
+as the last step when an instance of the structure
+is created, after the slots are initialized and
+the
+.code :init
+code, if any, has been executed. The registration
+takes place as if by the evaluation of the form
+.cblk
+.meti (finalize << obj (lambda <> (param) << body-form ...))
+.cble
+where
+.meta obj
+denotes the structure instance.
+
 .RE
 .PP