A question out of curiosity here, Is it possible to find the name of the method you are in ? Something like this where Magic should output "foo.bar.foobar" without resorting to a string literal.
with ada.text_io;
package body foo.bar is
function foobar return boolean is
begin
ada.text_io.put_line ("I am in :" & Magic);
return true;
end foobar;
end foo.bar;
I would assume this is information is located somewhere as similar is output for stack traces, exceptions and profiling tools etc, but i cannot find it documented anywhere!
As I'm sure you already know, Ada (unfortunately) doesn't support reflection.
However... if you're using GNAT and are okay with compiler-specific utilities, you can get this kind of information from the package GNAT.Source_Info.
Related
Posting for two reasons: (1) I was stuck on unhelpful compiler errors for far too long for such a simple issue and I want the next person to google those messages to come upon my (or other) answers, and (2) I still don't understand disallowing a use clause, so my own answer is really incomplete.
In order to call a program in two places with mostly the same arguments, I want to use the '&' to append to a default list inline:
declare
Exit_Code : constant Integer := GNAT.OS_Lib.Spawn (Program_Name => "gprbuild", Args => (Default_GPR_Arguments & new String'(File_Name_Parameter)));
begin
if Exit_Code /= 0 then
raise Program_Error with "Exit code:" & Exit_Code'Image;
end if;
end;
However, the compiler complains that System.Strings.String_List needs a use clause:
operator for type "System.Strings.String_List" is not directly visible
use clause would make operation legal
But inserting use System.Strings.String_List yields:
"System.Strings.String_List" is not allowed in a use clause
I also got this warning:
warning: "System.Strings" is an internal GNAT unit
warning: use "GNAT.Strings" instead
So I substituted GNAT for System in the with and the use clause and got an extra error in addition to the original 'you need a use clause for System.Strings.String_List' one:
"GNAT.Strings.String_List" is not allowed in a use clause
Why is GNAT.Strings.String_List not allowed in a use clause? Section 8.5 on use clauses doesn't seem to state anything on disallowed packages, so is this a compiler bug? Is it possible to define a new package that cannot have a use clause?
In a use clause of the form
use Name;
Name must be a package name. GNAT.Strings.String_List is a subtype name, not a package name.
There are a number of ways to invoke "&" for String_List. The simplest is to use the full name:
GNAT.Strings."&" (Left, Right)
but presumably you want to be able to use it as an operator in infix notation, Left & Right. Ways to achieve this, in decreasing specificity:
function "&" (Left : GNAT.Strings.String_List; Right : GNAT.Strings.String_List) return GNAT.Strings.String_List renames GNAT.Strings."&"; This makes this specific function directly visible.
use type GNAT.Strings.String_List; This makes all primitive operators of the type directly visible.
use all type GNAT.Strings.String_List; This makes all primitive operations of the type (including non-operator operations) directly visible.
use GNAT.Strings; This makes everything in the package directly visible.
Looks like it is a design decision. And many other packages in System follows this rule. From the s-string.ads (package specification for System.String):
-- Note: this package is in the System hierarchy so that it can be directly
-- be used by other predefined packages. User access to this package is via
-- a renaming of this package in GNAT.String (file g-string.ads).
My guess why this is done in that way: because it isn't in the Ada specification, but extension from GNAT.
I'm trying to do some basic translations of old C++ code from many moons ago to learn Ada, and I have been absolutely stumped on how to sort a vector using the built-in Generic_Sorting. I haven't been able to find any concrete examples of it in action, the closest being a now-defunct Danish wiki article which looks like it would have had a full example but the archive didn't snatch it up: https://web.archive.org/web/20100222010428/http://wiki.ada-dk.org/index.php/Ada.Containers.Vectors#Vectors.Generic_Sorting
Here is the code as I thought it should work from the above link:
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Containers.Vectors; use Ada.Containers;
procedure Vectortest is
package IntegerVector is new Vectors
(Index_Type => Natural,
Element_Type => Integer);
package IVSorter is new Generic_Sorting;
IntVec : IntegerVector.Vector;
Cursor : IntegerVector.Cursor;
begin
IntVec.Append(3);
IntVec.Append(43);
IntVec.Append(34);
IntVec.Append(8);
IVSorter.Sort(Container => IntVec);
Cursor := IntegerVector.First(Input);
while IntegerVector.Has_Element(Cursor) loop
Put(IntegerVector.Element(Cursor));
IntegerVector.Next(Cursor);
end loop;
end Vectortest;
I've tried so many different combinations of use and with but all I can get are various error codes. The above code gives Generic_Sorting is not visible, but when I try to explicitly state with Ada.Containers.Vectors.Generic_Sorting I get the error "Ada.Containers.Vectors.Generic_Sorting" is not a predefined library unit. I have no idea what I'm doing wrong here, I'm sure it's a fundamental misunderstanding of the way Ada brings in packages, and I hope that nailing this down will help me understand it a bit better.
Generic_Sorting is an inner package to Ada.Containers.Vectors and cannot be explicitly withed (as you have discovered). And since Ada.Containers.Vectors is itself a generic package, Generic_Sorting is an inner package to the instantiation of Ada.Containers.Vectors. So you can reach it by prefixing with the name of the instance:
package IVSorter is new IntegerVector.Generic_Sorting;
I want to print integers in Ada 83. At present I am just using 'with Text_IO' and 'use Text_IO'. I don't want to print using the Integer'Image option. I want to use Integer_Text_IO in ada83. Please help me out with the syntax.
I am using below code:
with Text_IO;
use Text_IO;
i: INTEGER :=1;
package Int_IO is new Integer_IO(INTEGER);
use Int_IO; put(i);
I am getting 'expect signed integer type in instantiation of "Num" ' error.
The example below, which compiles, should help.
But please, when posting a question on StackOverflow (or anywhere on the Net, really) show us the code you’ve actually tried. The sample you’ve provided doesn’t come close to compiling (it fails at line 3 with compilation unit expected), and that makes it very hard for us to work out how to help you.
You’ll get expect signed integer type in instantiation of “Num” if you try to instantiate Text_IO with the wrong sort of type (for example, Float).
with Text_IO;
procedure Integer_IO_Demo is
package Int_IO is new Text_IO.Integer_IO (Integer);
begin
for J in 5 .. 10 loop
Int_IO.Put (J);
Text_IO.New_Line;
end loop;
end Integer_IO_Demo;
I have just started using Ada, and I'm finding the generic package declarations to be rather silly. Maybe I'm not doing it right, so I'm looking for better options.
Take a look at the below example.
package STD_Code_Maps is new
Ada.Containers.Map(Key_Type => STD_Code_Type;
Element_Type => Ada.Strings.Unbounded.Unbounded_String);
STD_Code_Map : STD_Code_Maps.Map;
-- . . .
procedure Do_Something is
Item : Ada.Strings.Unbounded.Unbounded_String;
begin
Item := STD_Code_Maps.Element(STD_Code_Maps.First(STD_Code_Map));
-- Do something with the Item
-- . . .
end Do_Something;
It would be much cleaner to simply be able to write STD_Code_Map.First.Element instead of the godforsaken STD_Code_Maps.Element(STD_Code_Maps.First(STD_Code_Map));
Obviously I'm doing this wrong -- I think. I'm repeating the phrase STD_Code_Map at least thrice over there. I'm all for verbosity and everything, but really the code I'm writing seems bad and silly to me.
I was wondering if there is solution that doesn't require you to rename the package to something like package Map renames STD_Code_Maps; which would of course shorten the code but I don't want to do this on each and every procedure entry. I really think something like STD_Code_Map.First.Element would be much simpler. Can this be done in Ada 2012?
Note: Using the Unbounded_String package by default is also so difficult. Did the standard library designers actually give much thought to the ridiculous and overly long package hierarchy?
Thanks for reading this, and potentially helping me out. I'm new to Ada.
GNAT GPL 2012 and 2013, and FSF GCC 4.7 and 4.8, support the new container indexing scheme of Ada 2012, which means that you can write
Item := STD_Code_Map ({some Cursor});
And you can do this even with the -gnat05 switch to force Ada 2005 mode! (which has to be a bug).
Ada 2005 allows you to call a primitive function of a tagged type using object.function notation, provided that the first operand is of the tagged type; so you can write STD_Code_Map.First as shorthand for STD_Code_Maps.First (STD_Code_Map).
Putting these together, you can write
Item := STD_Code_Map (STD_Code_Map.First);
which is quite short!
The issue has nothing to do with generics. As Simon pointed out, you can say STD_Code_Map.First, since the type of STD_Code_Map is a tagged type and Ada supports this notation for tagged types. On the other hand, the type of STD_Code_Map.First is a Cursor type, which isn't tagged (making it tagged would have caused problems declaring certain operations that take both a Cursor and a Map). But even without the Ada 2012 container indexing that Simon mentioned, you can say
STD_Code_Maps.Element(STD_Code_Map.First);
which is a little better. Besides renaming a package, you can also rename the function:
function Elem (Position : STD_Code_Maps.Cursor) return STD_Code_Maps.Element_Type
renames STD_Code_Maps.Element;
and you can now use just Elem instead of STD_Code_Maps.Element wherever the renaming is directly visible. (You could call it Element if you want to. The renaming name can be the same or it can be different.) This could be helpful if you use that function a lot.
Ada was designed for readability and maintainability. (written once, read & maintained for much longer) This means that it does get a little verbose at times. If you prefer terse & cryptic there are plenty of other languages out there !
If you want to avoid typing STD_Code_Map all the time, just use a use clause:
use STD_Code_Map;
which would mean your code of
Item := STD_Code_Maps.Element(STD_Code_Maps.First(STD_Code_Map));
would become
Item := Element(First(STD_Code_Map));
Getting names nice and readable in Ada can sometimes be tricky. Often times language designers made the task worse than it had to be, by designing Ada standard library packages for use with Ada use clauses, without a thought to how they'd look to some poor sap who either can't or doesn't want to use that feature.
In this case though, there are things you can do on your own end.
For example "_Maps.Map" is redundant, so why not get rid of it from the package name? Why not use names so that you can write:
package STD_Code is new
Ada.Containers.Map(Key_Type => STD_Code_Type;
Element_Type => Ada.Strings.Unbounded.Unbounded_String);
Map : STD_Code.Map;
-- . . .
procedure Do_Something is
Item : Ada.Strings.Unbounded.Unbounded_String;
begin
Item := STD_Code.Element(STD_Code.First(Map));
-- Do something with the Item
-- . . .
end Do_Something;
Now Code looks like a bit of a null-meaning word too. Everything in a program is a code. So I'd consider ditching it as well. Unsually I name my Ada container packages something that says their basic theoretical function (eg: STD_to_String), while objects are more specific nouns.
Also, I should point out that if your map is constant and you can live with names that look like identifiers, often times you can get rid of maps to strings entirely by using an enumerated type and the 'image attribute.
If you're using Ada 2012 the STD_Code_Maps.Element(STD_Code_Maps.First(STD_Code_Map)); could become:
Function Get_First( Map : STD_Code_Maps.Map ) return Unbounded_String is
( STD_Code_Maps.Element(Map.First) );
That is an example of the new Expression-functions, which were mainly introduced for pre- and post-conditions.
Of course, if you're using Ada 2012 then the precise map you'd likely want is Ada.Containers.Indefinite_Ordered_Maps -- the Indefinite_* containers are those that [can] have indefinite elements, like String.
In addition to TED's comment, using an enumeration when the maps are constant have even more advantages, namely case coverage: the compiler will flag as an error any case-statement that doesn't cover all alternatives. So if you add a new code it will flag all the case-statements that you need to modify. (Of course this benefit is lost when you use the others case.)
What is a purpose in Pascal to declare variable that is pointer to a pointer? I have a code in Mac Think Pascal. Here is some parts from the code that I don't understand:
type
my_array = array[1..100] of integer;
my_array_pointer = ^my_array;
my_array_handle = ^my_array_pointer;
...
var
xx : my_array_handle;
...
begin
xx:= my_array_handle(NewHandle( sizeof(my_array)) );
As you see, the last line is an assignment of a type my_array_handle to variable xx. What does it mean? What does NewHandle function do? (This is an internal function of Think Pascal). Actually, I need to convert a Think Pascal program to Windows Pascal. However I cannot find the description of NewHandle function, and don't know how to implement this function using the standard (New(), GetMem() etc) pointer functions.
This is a classic macos feature, not typically something of Pascal.
I don't know exactly, but it had something to do with relocatability of the loaded program in a non PM environment.
Note that the indirect pointer is allocated via an OS function, which probably means that it is allocated in some table that is maintained by the OS. (so that the OS can move/relocate the program?)
In modern Mac (and other) programming this whole principle is alien. Just clean it up.
(added)
If you want to keep these redirections, you could try your luck with something like:
function newhandle( nrbytes:integer):ppointer;
var xx : ppointer;
begin
new(xx);
getmem(xx^,nrbytes);
newhandle:=xx;
end;
I didn't add this originally, but I recommend you simply clean up these anachronistic indirect references and use my_array_pointer based pointers and getmem or new directly.
The meaning of these indirect references has no use on non m68k Classic Mac OS systems, though afaik later PPC versions still somewhat support them. (PPC is always protected mode)
If you really want the gritty details, you probably want to subscribe to the mac-pascal list.