cannot create an instance of subset type
Hi,
Using the next code I get an error on the instantiation of $d2;
---
use v6;
class ABC {
method s ( Int $i ) { say $i + 10; }
}
subset DEF of ABC;
my ABC $a .= new;
$a.s(10); # 20
my DEF $d1 = $a;
$d1.s(11); # 21
my DEF $d2 .= new;
$d2.s(12);
---
Error is
You cannot create an instance of this type (DEF)
in block at xt/subset-test.pl6 line 15
Why is this?
Regards,
Marcel
Re: cannot create an instance of subset type
Subset types are not object types.
A subset is basically a bit of checking code and base type associated with
a new type name.
In something like:
my ABC $a .= new;
That is exactly the same as:
my ABC $a = ABC.new;
Well there is no functional `.new` method on any subset types, so
`DEF.new()` isn't going to do anything.
DEF.new # ERROR
---
The worst part of your code is that you are using a `subset` without a
`where` clause. Which is almost completely pointless.
I honestly think that there is an argument to be made that it shouldn't
even be possible to write a `subset` without a `where` clause.
It isn't like other languages where you can create something like a
lightweight clone or lightweight subclass of a type.
It also isn't an alias.
It's whole purpose is to attach a `where` clause as an extra check to type
based things.
If you want an alias, use an alias
my constant DEF = ABC;
my constant DEF = ABC:D;
If you want a lightweight subclass, create a lightweight subclass.
my class DEF is ABC {}
If you want an extra check, then and only then does it make sense to use a
`subset`.
my subset GHI of Int where -10 ≤ $_ ≤ 10;
---
A `subset` without a `where` clause only makes certain language features
become unavailable.
Unless that is exactly what you want to accomplish, use something else.
On Fri, Jul 10, 2020 at 3:18 PM Marcel Timmerman wrote:
> Hi,
>
> Using the next code I get an error on the instantiation of $d2;
>
> ---
> use v6;
>
> class ABC {
>method s ( Int $i ) { say $i + 10; }
> }
>
> subset DEF of ABC;
>
> my ABC $a .= new;
> $a.s(10); # 20
>
> my DEF $d1 = $a;
> $d1.s(11); # 21
>
> my DEF $d2 .= new;
> $d2.s(12);
> ---
>
> Error is
>
> You cannot create an instance of this type (DEF)
>in block at xt/subset-test.pl6 line 15
>
> Why is this?
>
> Regards,
> Marcel
>
Raku-LibCurl:ver<1.0> install error on older MacOS?
Hello, I just updated to Rakudo-2020.06, and while updating many of my modules to their latest versions I saw an error installing/updating (Raku) LibCurl. Below, the first few lines of the error seen with LibCurl::Easy (and EasyHandle): ===> Testing: LibCurl:ver<1.0>:auth:api<1> [LibCurl] # Failed test 'LibCurl::EasyHandle module can be use-d ok' [LibCurl] # at t/01-load.t line 6 [LibCurl] # Cannot load native library 'libcurl.so.4' [LibCurl] # Failed test 'LibCurl::Easy module can be use-d ok' [LibCurl] # at t/01-load.t line 8 [LibCurl] # ===SORRY!=== Error while compiling /Users/myuseraccount/.zef/store/raku-libcurl.git/random_40-character-alphanumeric/lib/LibCurl/Easy.rakumod (LibCurl::Easy) [LibCurl] # Cannot load native library 'libcurl.so.4' [LibCurl] # at /Users/myuseraccount/.zef/store/raku-libcurl.git/random_40-character-alphanumeric/lib/LibCurl/Easy.rakumod (LibCurl::Easy):2 So one caveat is that this install is on an OS which many would consider to be "MacOS.10.ancient" [I'm posting here and not on Github because we seem to have a number of Mac users on this mailing-list]. But the fact of the matter is Raku LibCurl:ver<0.9> worked just fine with Rakudo-2020.02.1. Furthermore, now that I've downgraded back to Raku LibCurl:ver<0.9>, LibCurl::Easy works once again on the latest Rakudo-2020.06. So I really feel the problem is with LibCurl:ver<1.0> on Macs, and not my particular install. Questions for Mac-heads: Do newer versions of MacOS still install LibCurl as part of the OS? Where does that reside? I know I have libcurl in the following directories, however 'libcurl.so.4' is conspicuously absent: /opt/local/lib/libcurl.4.dylib /opt/local/lib/libcurl.a /opt/local/lib/libcurl.dylib Are Mac-users able to use (Raku) LibCurl:ver<1.0> on their (newer) systems? FYI, I've installed curl independently of MacOS via either MacBrew or MacPorts, and in fact MacBrew reports upon attempting to update: "Warning: curl 7.71.1 is already installed and up-to-date". Any help appreciated, Thx, Bill.
