The following example taken from https://dlang.org/library/std/algorithm/comparison/pred_switch.html

doesn't compile under gdc...Is there a way to fix it ?


int factorial(int n)
{
    return n.predSwitch!"a <= b"(
        -1, {throw new Exception("Can not calculate n! for n < 0");}(),
        0, 1, // 0! = 1
        n * factorial(n - 1) // n! = n * (n - 1)! for n >= 0
        );
}
writeln(factorial(3));

The gdc compiler error is
 error: no property 'predSwitch' for type 'int'
     return n.predSwitch!"a <= b"(

On 7/29/20 5:46 PM, Andy Balba wrote:
> 
> The following example taken from https://dlang.org/library/std/algorithm/comparison/pred_switch.html
> 
> doesn't compile under gdc...Is there a way to fix it ?
> 
> 
> int factorial(int n)
> {
>      return n.predSwitch!"a <= b"(
>          -1, {throw new Exception("Can not calculate n! for n < 0");}(),
>          0, 1, // 0! = 1
>          n * factorial(n - 1) // n! = n * (n - 1)! for n >= 0
>          );
> }
> writeln(factorial(3));
> 
> The gdc compiler error is
>   error: no property 'predSwitch' for type 'int'
>       return n.predSwitch!"a <= b"(
> 

Are you importing std.algorithm.comparison?

This kind of question probably belongs on the learn forum.

-Steve

On Wednesday, 29 July 2020 at 21:46:04 UTC, Andy Balba wrote:
>
> The following example taken from https://dlang.org/library/std/algorithm/comparison/pred_switch.html
>
> doesn't compile under gdc...Is there a way to fix it ?
>
>
> int factorial(int n)
> {
>     return n.predSwitch!"a <= b"(
>         -1, {throw new Exception("Can not calculate n! for n < 0");}(),
>         0, 1, // 0! = 1
>         n * factorial(n - 1) // n! = n * (n - 1)! for n >= 0
>         );
> }
> writeln(factorial(3));
>
> The gdc compiler error is
>  error: no property 'predSwitch' for type 'int'
>      return n.predSwitch!"a <= b"(

Your release of GDC seems to use a very old version of Phobos.
You need to have Phobos >= 2.067 (released in 2015) for this to work, see e.g. https://run.dlang.io/is/cAFJoB
On Ubuntu/Debian you should be able to at least get a GDC libphobos of 2.076.

Alternatively, as you might expect it works in dmd or ldc: https://run.dlang.io/is/CpFfkQ