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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/ref/api-data.texi | 87 |
1 files changed, 18 insertions, 69 deletions
diff --git a/doc/ref/api-data.texi b/doc/ref/api-data.texi index 7b10d34f4..7e36f7446 100644 --- a/doc/ref/api-data.texi +++ b/doc/ref/api-data.texi @@ -1,6 +1,6 @@ @c -*-texinfo-*- @c This is part of the GNU Guile Reference Manual. -@c Copyright (C) 1996, 1997, 2000-2004, 2006-2016 +@c Copyright (C) 1996, 1997, 2000-2004, 2006-2017 @c Free Software Foundation, Inc. @c See the file guile.texi for copying conditions. @@ -8757,7 +8757,6 @@ records in Guile are implemented with structures. * Vtable Contents:: * Meta-Vtables:: * Vtable Example:: -* Tail Arrays:: @end menu @node Vtables @@ -8808,8 +8807,7 @@ Scheme level. This can be used for fields which should only be used from C code. @end itemize -Here are some examples. @xref{Tail Arrays}, for information on the -legacy tail array facility. +Here are some examples. @example (make-vtable "pw") ;; one writable field @@ -8840,12 +8838,11 @@ structure. @node Structure Basics @subsubsection Structure Basics -This section describes the basic procedures for working with -structures. @code{make-struct} creates a structure, and -@code{struct-ref} and @code{struct-set!} access its fields. +This section describes the basic procedures for working with structures. +@code{make-struct/no-tail} creates a structure, and @code{struct-ref} +and @code{struct-set!} access its fields. -@deffn {Scheme Procedure} make-struct vtable tail-size init @dots{} -@deffnx {Scheme Procedure} make-struct/no-tail vtable init @dots{} +@deffn {Scheme Procedure} make-struct/no-tail vtable init @dots{} Create a new structure, with layout per the given @var{vtable} (@pxref{Vtables}). @@ -8855,25 +8852,22 @@ put values in read-only fields. If there are fewer @var{init} arguments than fields then the defaults are @code{#f} for a Scheme field (type @code{p}) or 0 for an uninterpreted field (type @code{u}). -Structures also have the ability to allocate a variable number of -additional cells at the end, at their tails. However, this legacy -@dfn{tail array} facilty is confusing and inefficient, and so we do not -recommend it. @xref{Tail Arrays}, for more on the legacy tail array -interface. +The name is a bit strange, we admit. The reason for it is that Guile +used to have a @code{make-struct} that took an additional argument; +while we deprecate that old interface, @code{make-struct/no-tail} is the +new name for this functionality. -Type @code{s} self-reference fields, permission @code{o} opaque -fields, and the count field of a tail array are all ignored for the -@var{init} arguments, ie.@: an argument is not consumed by such a -field. An @code{s} is always set to the structure itself, an @code{o} -is always set to @code{#f} or 0 (with the intention that C code will -do something to it later), and the tail count is always the given -@var{tail-size}. +Type @code{s} self-reference fields and permission @code{o} opaque +fields are ignored for the @var{init} arguments, ie.@: an argument is +not consumed by such a field. An @code{s} is always set to the +structure itself and an @code{o} is always set to @code{#f} or 0 (with +the intention that C code will do something to it later). For example, @example (define v (make-vtable "prpwpw")) -(define s (make-struct v 0 123 "abc" 456)) +(define s (make-struct/no-tail v 123 "abc" 456)) (struct-ref s 0) @result{} 123 (struct-ref s 1) @result{} "abc" @end example @@ -8886,6 +8880,8 @@ There are a few ways to make structures from C. @code{scm_make_struct} takes a list, @code{scm_c_make_struct} takes variable arguments terminated with SCM_UNDEFINED, and @code{scm_c_make_structv} takes a packed array. + +For all of these, @var{tail_size} should be zero (as a SCM value). @end deftypefn @deffn {Scheme Procedure} struct? obj @@ -9197,53 +9193,6 @@ cases, the records facility is usually sufficient. But sometimes you need to make new kinds of data abstractions, and for that purpose, structs are here. -@node Tail Arrays -@subsubsection Tail Arrays - -Guile's structures have a facility whereby each instance of a vtable can -contain a variable-length tail array of values. The length of the tail -array is stored in the structure. This facility was originally intended -to allow C code to expose raw C structures with word-sized tail arrays -to Scheme. - -However, the tail array facility is confusing and doesn't work very -well. It is very rarely used, but it insinuates itself into all -invocations of @code{make-struct}. For this reason the clumsily-named -@code{make-struct/no-tail} procedure can actually be more elegant in -actual use, because it doesn't have a random @code{0} argument stuck in -the middle. - -Tail arrays also inhibit optimization by allowing instances to affect -their shapes. In the absence of tail arrays, all instances of a given -vtable have the same number and kinds of fields. This uniformity can be -exploited by the runtime and the optimizer. The presence of tail arrays -make some of these optimizations more difficult. - -Finally, the tail array facility is ad-hoc and does not compose with the -rest of Guile. If a Guile user wants an array with user-specified -length, it's best to use a vector. It is more clear in the code, and -the standard optimization techniques will do a good job with it. - -That said, we should mention some details about the interface. A vtable -that has tail array has upper-case permission descriptors: @code{W}, -@code{R} or @code{O}, correspoding to tail arrays of writable, -read-only, or opaque elements. A tail array permission descriptor may -only appear in the last element of a vtable layout. - -For exampple, @samp{pW} indicates a tail of writable Scheme-valued -fields. The @samp{pW} field itself holds the tail size, and the tail -fields come after it. - -@example -(define v (make-vtable "prpW")) ;; one fixed then a tail array -(define s (make-struct v 6 "fixed field" 'x 'y)) -(struct-ref s 0) @result{} "fixed field" -(struct-ref s 1) @result{} 2 ;; tail size -(struct-ref s 2) @result{} x ;; tail array ... -(struct-ref s 3) @result{} y -(struct-ref s 4) @result{} #f -@end example - @node Dictionary Types @subsection Dictionary Types |