* Generics and I/O @ 1998-10-02 0:00 William L Hayhurst 1998-10-03 0:00 ` Niklas Holsti ` (2 more replies) 0 siblings, 3 replies; 5+ messages in thread From: William L Hayhurst @ 1998-10-02 0:00 UTC (permalink / raw) Hi there. I have a question about Generics and IO. Given generic type Item is private; package Foo is -- ... -- procedure Print is -- ... -- Put( Item ); -- ... -- end Print; end Foo; My compiler ( GNAT ) will flag the Put( Item ) as an error. So if I instantiate foo as declare -- ... -- with Foo; use Foo; package Int_Foo is new Foo ( Item => Integer ); use Int_Foo; -- ... -- end; and the Put( ) still won't work, even if a declare a new Int_IO package in the scope of Foo::Print. So do I have to overload Put( ) inside package foo? Thanks in advance! --Lyle ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Generics and I/O 1998-10-02 0:00 Generics and I/O William L Hayhurst @ 1998-10-03 0:00 ` Niklas Holsti 1998-10-03 0:00 ` Dmitriy Anisimkov 1998-10-06 0:00 ` Robert I. Eachus 2 siblings, 0 replies; 5+ messages in thread From: Niklas Holsti @ 1998-10-03 0:00 UTC (permalink / raw) William L Hayhurst wrote: > > Hi there. I have a question about Generics and IO. Given > > generic > type Item is private; > package Foo is > -- ... -- > procedure Print is > -- ... -- > Put( Item ); > -- ... -- > end Print; > end Foo; > > My compiler ( GNAT ) will flag the Put( Item ) as an error. [ rest snipped ] GNAT is correct; no Put operation is visible where you try to call it, in the generic. You need to supply a Put. Since the Item type is private, you should include this Put as a generic formal parameter: generic type Item is private; with procedure Put (I : in Item); package Foo is procedure Print (I : in Item); end Foo; Then, when you instantiate your generic, you supply the Put operation to be used, as shown in the code example below. I've used an enumeration type for Item, but I hope you get the point and can do the same for Integer. Note that it's not necessary to have a "wrapper" operation like MyPut. By placing the proper specification for "Put" in the generic part, you could instantiate Foo with MyItem_IO.Put directly. However, the Text_IO Put operations have additional parameters, such as Width, that must be included in the generic Foo Put specification for this to work. The instantiation can also find a suitable Put "automagically" by using the "<>" symbol in the generic spec, but I won't go into that. Hope this helps, - Niklas with Foo; with Text_IO; procedure Main is type MyItem is (This, That, TheOther); package MyItem_IO is new Text_IO.Enumeration_IO (MyItem); procedure MyPut (I : in MyItem) is begin Text_IO.Put ("MyPut: "); MyItem_IO.Put (I); Text_IO.New_Line; end MyPut; package MyFoo is new Foo (MyItem, MyPut); begin MyFoo.Print (That); end Main; ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Generics and I/O 1998-10-02 0:00 Generics and I/O William L Hayhurst 1998-10-03 0:00 ` Niklas Holsti @ 1998-10-03 0:00 ` Dmitriy Anisimkov 1998-10-06 0:00 ` Robert I. Eachus 2 siblings, 0 replies; 5+ messages in thread From: Dmitriy Anisimkov @ 1998-10-03 0:00 UTC (permalink / raw) if you Item is a scalar type then : with Text_IO; > generic > type Item is private; > package Foo is > -- ... -- procedure Print(Value : Item) is > -- ... -- Text_IO.Put( Value'Image ); > -- ... -- > end Print; > end Foo; if you Item is only integer type then : with Ada.Text_IO.Integer_IO; > generic type Item is range <>; -- must be > package Foo is > -- ... -- package Item_IO is new Ada.Text_IO.Integer_IO(Item); -- instantiation use Item_IO; procedure Print(Value : Item) is -- must be > -- ... -- Put( Value ); -- must be > -- ... -- > end Print; > end Foo; ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Generics and I/O 1998-10-02 0:00 Generics and I/O William L Hayhurst 1998-10-03 0:00 ` Niklas Holsti 1998-10-03 0:00 ` Dmitriy Anisimkov @ 1998-10-06 0:00 ` Robert I. Eachus 1998-10-07 0:00 ` Dale Stanbrough 2 siblings, 1 reply; 5+ messages in thread From: Robert I. Eachus @ 1998-10-06 0:00 UTC (permalink / raw) Add the following: generic type Item is private; -- with procedure Put(I: in Item) is <>; -- package Foo is... Now if there is a visible Put procedure which matches the profile, you are all set. Otherwise you will have to pass it during the instantiation explicity: with Ada.Integer_Text_IO; package Int_Foo is new Foo(Integer,Ada.Integer_Text_IO.Put); -- Robert I. Eachus with Standard_Disclaimer; use Standard_Disclaimer; function Message (Text: in Clever_Ideas) return Better_Ideas is... ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Generics and I/O 1998-10-06 0:00 ` Robert I. Eachus @ 1998-10-07 0:00 ` Dale Stanbrough 0 siblings, 0 replies; 5+ messages in thread From: Dale Stanbrough @ 1998-10-07 0:00 UTC (permalink / raw) Robert I. Eachus wrote: "Now if there is a visible Put procedure which matches the profile, you are all set. Otherwise you will have to pass it during the instantiation explicity: with Ada.Integer_Text_IO; package Int_Foo is new Foo(Integer,Ada.Integer_Text_IO.Put);" But that won't work, because ada.integer_text_Io.put has a 2nd parameter, the width field. If you want to do this (which i did recently), you have to write a wrapper procedure which creates a bridge between the simple profile that the generic expects, and any parameters that the "real" procedure has. E.g. Generic expects procedure... procedure Put (Item : Element); Ada.Integer_Text_IO.Put has... procedure Put (Item : Integer; Width : Natural); So you need a procedure... procedure Put (Item : Integer) is begin Ada.Integer_Text_IO.Put (Item, Ada.Integer_Text_IO.Default_Width); end; Dale ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~1998-10-07 0:00 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 1998-10-02 0:00 Generics and I/O William L Hayhurst 1998-10-03 0:00 ` Niklas Holsti 1998-10-03 0:00 ` Dmitriy Anisimkov 1998-10-06 0:00 ` Robert I. Eachus 1998-10-07 0:00 ` Dale Stanbrough
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