Re: Gnat bug or mistaken program?

[Richard Iswara <haujekchifan@gmail.com>]

On 21/07/2021 23.56, Shark8 wrote:
> On Wednesday, July 21, 2021 at 2:29:22 AM UTC-6, Jeffrey R. Carter wrote:
>>> Thank you. So it is a visibility problem.
>> "Understanding visibility is the key to understanding Ada." -- /Ada Distilled/
>>
>> Recommending the use package clause as a solution to a misunderstanding of
>> visibility is a disservice to a beginning user. Widespread application of use
>> pkg clauses is a crutch to avoid understanding visibility. I recommend that
>> those who do not understand visibility avoid the use clause altogether, as this
>> forces them to learn about visibility. When one understands visibility, one can
>> then make reasoned decisions about whether and when to add use clauses.
>>
>> In decreasing order of specificity, the ways to call an operation in a pkg are
>>
>> * Use the full name: Ada.Numerics.Elementary_Functions."**" (10.0, Logs)
>> This calls the operation once without changing its visibility
>> * Rename the operation:
>> function "**" (Left : Float; Right : Float) return Float renames
>> Ada.Numerics.Elementary_Functions."**";
>> This makes the specific operation visible
>> * Use type: this makes all operators of the type visible (not applicable
>> in this case)
>> * Use all type: this makes all operations of the type visible (not
>> applicable in this case)
>> * Use package: this makes everything in the package visible
>>
>> Use pkg is clearly overkill for this case, and overuse of it can have negative
>> consequences.
>>
>> -- 
>> Jeff Carter
>> "Choose a data representation that
>> makes the program simple."
>> Elements of Programming Style
>> 188
> 
> This is excellent advice and an good list, though the last element should be two or three:
> * Local, via declare-region/-scope; and
> * ["local" via usage inside the spec, (perhaps in the public portion, perhaps in the private); and]
> * Global (top of the file context-clauses).
> 

Thank you all for your tips and explanations.