Boolean Operation on pointer (access)

Boolean Operation on pointer (access)

[Dominic D'Apice]

Hi,


When i try to do this :

x := ppp (x,z); --where x is a access type and ppp return a access 

if (x /= null) then  --the line where the compiler stop

    zzz (x,z);
else   
    aaa (q,r);
end if;


I got this error :

gerer_location.ada: Error: line 136 col 23 LRM:8.4(1), 
Binary operator "/=" not directly visible, use clause or conversion
might be needed 


The operation "/=" should be permit on pointer, then why i got this
error ?

Thanks
Dominic

Re: Boolean Operation on pointer (access)

[Robert A Duff]

"Dominic D'Apice" <dapiced@sympatico.ca> writes:

> if (x /= null) then  --the line where the compiler stop
...
> I got this error :
> 
> gerer_location.ada: Error: line 136 col 23 LRM:8.4(1), 
> Binary operator "/=" not directly visible, use clause or conversion
> might be needed 
> 
> The operation "/=" should be permit on pointer, then why i got this
> error ?

You want a "use type" clause on the pointer type.

Yes, "/=" is allowed on pointers, but this operator is implicitly
declared at a certain place in the program, and you need to make it
directly visible in order to call it.

- Bob

RE: Boolean Operation on pointer (access)

[Dominic D'Apice]

Ok then, i use the clause use in my .ada for my package ads, it's
working, 
but i don't understand why i need to put a use clause for only this king
of operator ?

For the rest of my .ada program  i only precede each thing by the .ads
package name 
Ex : package.var := xxx;

Thanks
Dominic

-----Original Message-----
From: comp.lang.ada-admin@ada.eu.org
[mailto:comp.lang.ada-admin@ada.eu.org] On Behalf Of Robert A Duff
Sent: 26 octobre, 2002 21:08
To: comp.lang.ada@ada.eu.org
Subject: Re: Boolean Operation on pointer (access)


"Dominic D'Apice" <dapiced@sympatico.ca> writes:

> if (x /= null) then  --the line where the compiler stop
...
> I got this error :
> 
> gerer_location.ada: Error: line 136 col 23 LRM:8.4(1),
> Binary operator "/=" not directly visible, use clause or conversion
> might be needed 
> 
> The operation "/=" should be permit on pointer, then why i got this 
> error ?

You want a "use type" clause on the pointer type.

Yes, "/=" is allowed on pointers, but this operator is implicitly
declared at a certain place in the program, and you need to make it
directly visible in order to call it.

- Bob
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Re: Boolean Operation on pointer (access)

[Robert A Duff]

"Dominic D'Apice" <dapiced@sympatico.ca> writes:

> Ok then, i use the clause use in my .ada for my package ads, it's
> working, 
> but i don't understand why i need to put a use clause for only this king
> of operator ?
> 
> For the rest of my .ada program  i only precede each thing by the .ads
> package name 
> Ex : package.var := xxx;

You could say:

    if Package_Name."/="(X, null) then...

but you wouldn't want to.  You want to say:

    if X /= null then...

which is equivalent to:

    if "/="(X, null) then ...

so you need the "use type".  Does that make sense?

- Bob

Re: Boolean Operation on pointer (access)

[Jeffrey Carter]

Dominic D'Apice wrote:
> Ok then, i use the clause use in my .ada for my package ads, it's
> working, 
> but i don't understand why i need to put a use clause for only this king
> of operator ?
> 
> For the rest of my .ada program  i only precede each thing by the .ads
> package name 
> Ex : package.var := xxx;

The things in a package mentioned in a context clause ("with") are not 
directly visible. This means you have to precede them with the package 
name to reference them.

You can make everything in a package directly visible by naming the 
package in a use clause. Instead of

X : Package_Name.Var;

X := Package_Name."+" (X, 1);

you can have

use Package_Name;

X : Var;

X := X + 1;

This is not always desirable. To only make the operators of a specific 
type from the package visible, you can name the type in a "use type" clause:

use type Package_Name.Var;

X : Package_Name.Var; -- "Package_Name." needed here

X := X + 1; -- "+" is an operator for Var, so not needed here

-- 
Jeff Carter
"Why don't you bore a hole in yourself and let the sap run out?"
Horse Feathers