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  • Rosetta Code task Proper divisors fails to compile

    From Kenneth Wolcott@21:1/5 to All on Tue Jul 25 21:49:49 2023
    Hi;

    Trying to understand (and use) a Rosetta Code task (Proper divisors)...

    https://rosettacode.org/wiki/Proper_divisors#Ada

    it fails to compile

    gnatmake -vh ./proper_divisors.adb

    GNATMAKE 13.1.0
    Copyright (C) 1992-2023, Free Software Foundation, Inc.
    "proper_divisors.ali" being checked ...
    -> "proper_divisors.ali" missing.
    gcc -c -I./ -I- ./proper_divisors.adb
    generic_divisors.ads:11:08: error: (Ada 2005) cannot copy object of a limited type (RM-2005 6.5(5.5/2))
    generic_divisors.ads:11:08: error: return by reference not permitted in Ada 2005
    End of compilation
    gnatmake: "./proper_divisors.adb" compilation error

    Why does this work for the the submitter of the Rosetta Code task and not for me?

    Thanks,
    Ken Wolcott

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  • From Jeffrey R.Carter@21:1/5 to Kenneth Wolcott on Wed Jul 26 10:36:12 2023
    On 2023-07-26 06:49, Kenneth Wolcott wrote:

    https://rosettacode.org/wiki/Proper_divisors#Ada

    gnatmake -vh ./proper_divisors.adb

    generic_divisors.ads:11:08: error: (Ada 2005) cannot copy object of a limited type (RM-2005 6.5(5.5/2))
    generic_divisors.ads:11:08: error: return by reference not permitted in Ada 2005

    Why does this work for the the submitter of the Rosetta Code task and not for me?

    For some reason your gnatmake seems to be defaulting to -gnat05 mode. This code has an expression function, which is Ada 12, so try adding -gnat12 to the command.

    You also should not need to put "./" in front of the file name, though I don't see how that would make a difference.

    --
    Jeff Carter
    "I'm a lumberjack and I'm OK."
    Monty Python's Flying Circus
    54

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  • From Kenneth Wolcott@21:1/5 to Jeffrey R.Carter on Wed Jul 26 11:30:12 2023
    On Wednesday, July 26, 2023 at 1:36:15 AM UTC-7, Jeffrey R.Carter wrote:
    For some reason your gnatmake seems to be defaulting to -gnat05 mode. This code
    has an expression function, which is Ada 12, so try adding -gnat12 to the command.

    You also should not need to put "./" in front of the file name, though I don't
    see how that would make a difference.

    Hi Jeff;

    Thank you for your suggestion. Doesn't seem to have any effect.

    (*SIGH*)

    gnatmake -vh -gnat2012 proper_divisors.adb

    GNATMAKE 13.1.0
    Copyright (C) 1992-2023, Free Software Foundation, Inc.
    "proper_divisors.ali" being checked ...
    -> "proper_divisors.ali" missing.
    gcc -c -gnat2012 proper_divisors.adb
    generic_divisors.ads:11:08: error: (Ada 2005) cannot copy object of a limited type (RM-2005 6.5(5.5/2))
    generic_divisors.ads:11:08: error: return by reference not permitted in Ada 2005
    End of compilation
    gnatmake: "proper_divisors.adb" compilation error

    Ken

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  • From Jeffrey R.Carter@21:1/5 to Kenneth Wolcott on Wed Jul 26 21:57:37 2023
    On 2023-07-26 20:30, Kenneth Wolcott wrote:

    Thank you for your suggestion. Doesn't seem to have any effect.

    Interesting. I get the same results with GNAT 12.

    Looking more closely at the code, I think the error, while its msg is misleading, is correct. A function that returns a limited type can only return an aggregate, a function call, or an object declared by an extended return statement. The generic formal object None is none of these.

    Changing the generic parameter to a function

    with function None return Result_Type;

    makes the code correct. You need to change the definition of Empty in Proper_Divisors

    function Empty return Pos_Arr is (1 .. 0 => <>);

    and create a function to supply for the 2nd instantiation

    function None return Natural is (0);
    ...
    package Divisor_Count is new Generic_Divisors
    (Result_Type => Natural, None => None, One => Cnt, Add => "+");

    and then it compiles and runs.

    Another possibility is to make Result_Type simply private, though that is slightly less general. That may be how the OP got the code to compile and run. It might be that limited was added later because the OP saw that it could be, and never tested the change.

    --
    Jeff Carter
    "I'm a lumberjack and I'm OK."
    Monty Python's Flying Circus
    54

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  • From Kenneth Wolcott@21:1/5 to Jeffrey R.Carter on Wed Jul 26 15:26:28 2023
    On Wednesday, July 26, 2023 at 12:57:40 PM UTC-7, Jeffrey R.Carter wrote:
    On 2023-07-26 20:30, Kenneth Wolcott wrote:

    Thank you for your suggestion. Doesn't seem to have any effect.
    Interesting. I get the same results with GNAT 12.

    Looking more closely at the code, I think the error, while its msg is misleading, is correct. A function that returns a limited type can only return
    an aggregate, a function call, or an object declared by an extended return statement. The generic formal object None is none of these.

    Changing the generic parameter to a function

    with function None return Result_Type;

    makes the code correct. You need to change the definition of Empty in Proper_Divisors

    function Empty return Pos_Arr is (1 .. 0 => <>);

    and create a function to supply for the 2nd instantiation

    function None return Natural is (0);
    ...
    package Divisor_Count is new Generic_Divisors
    (Result_Type => Natural, None => None, One => Cnt, Add => "+");

    and then it compiles and runs.

    Another possibility is to make Result_Type simply private, though that is slightly less general. That may be how the OP got the code to compile and run.
    It might be that limited was added later because the OP saw that it could be,
    and never tested the change.

    Hi Jeff;

    Thank you for your reply.

    I went with the latter suggestion for my local use.

    Ken

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