Here is a package that implements a type of String. Each String can have wasted space. Unlike with Ada.Strings.Bounded.Bounded String, there is not a need to know what the maximum length of a string is. Unlike GNAT's Unbounded_String's,the package could be significantly faster. This following design could have 'SV' compiled if there was no "out" in the record. That "out" is a new proposed feature that provides a way of making data entities be read-only. The "out" is there to make the component named "Ptr" be read-only. An aim here is to get convenient access to every byte in the SV String's 'Ptr.all' whilst avoiding a use of the Controlled types that are in Unbounded Strings. Unbounded Strings are slow and SV Strings could be faster and possibly a lot faster (in GNAT). But the language maybe does not have the right features needed. ------------------------------------------------------------- procedure Test is package SV is type String_Access is access all String; Null_String_Access : constant String_Access; type Vstr is limited record Ptr : out String_Access := Null_String_Access; Len : Natural := 0; end record; procedure Free (X : in out Vstr); function "+" (Source : Vstr) return String; -- pragma Inline ("+"); private Null_String_Access : constant String_Access := new String (1 .. 0); end SV; package body SV is ... end SV; X, Y : SV.Vstr; begin -- All these 4 cases are legal and illegal in the way needed X := Y; -- Illegal due to the 'limited' and the 'out' X.Len := Y.Len; -- Legal X.Ptr.all := Y.Ptr.all; -- Legal. Better than Unbounded_String style X.Ptr := Y.Ptr; -- Illegal because the LHS is read-only due to -- the use of the "out" keyword. end Test; ------------------------------------------------------------- Without the "out" there would be a problem, which is that a package with-ing the SV package can do this: A.Len := B.Len; A.Ptr := B.Ptr; That last line involves the copying of a pointer. The designer of the SV package wants to stop copying of pointers (then the user is less likely to have a problem when reclaiming the memory of both A and B. If the "String_Access" type were instead defined by: type String_Access is access constant String; then that, allows assigning to A.Ptr and it stops assigning to A.Ptr.all. That is swapped from what is wanted. To make Ptr be 'limited private' stops initialising since it is limited. To make Ptr private stops the user from writing "Ptr.all". A function can return the value of the "Ptr" component. But then ".all" can't be appended to a function (but a feature like that could be nice). Something like this has to be written. This this has an extra line: AR := Ref_Val (A); AR.all := B.Ptr.all; A.Len := B.Len; The default mode for records can be an "in out" mode. A synonym for "in out" can be "var" or "ref". If package spec variables default to being "out" then there could be a lot of variables that can be written to. Big systems with read-write access to thousands of variables, most of which only need to be available read-only, are going to be less safe. How can Ada be advocated to an optimum degree if another language allows read only publishing of the values of data objects. At the Ada-Comment, there was a man from Boeing that said that the certifier required no inlining. Perhaps due to bugs (maybe including optimiser bugs). That person said privately to me that a compiler already allowed the exporting in a read only way, of variables in a package spec. However it was done with a pragma. Does anybody know the names of compilers allowing read only exporting of data that is variable inside the package body ?. Here is an example of a new design I propose. "var" is a synonym for "in out". Some global option(s) allow switching between "in out" mode and the read-only "out" mode. package Q is X : var Integer := 0; -- packages with-ing Q can write to Q.X end Q; --------------------------------- I could have e-mailed this to Ada-Comment @ adaic.org. Top vendors (ACT, and some others were unclear) were at that list declaring briefly that Ada does not need a read-only feature since inlining is possible and so is asking users to add ".all" to each var, and also there is an export/import option. Here is a URL of the Ada-Comment list (that is moderated by Mr R. Brukardt) (I guess people didn't know it was there): http://www.adaic.org/standards/ada95.html What are the arguments in favour of prohibiting variables and record components from having their values be 'published in a read only way' ?. I guess we don't know. ______________ Craig Carey Auckland Mailing Lists: http://www.ijs.co.nz/ada_95.htm