Re: Is std.variant.visit not @nogc?
On 4/10/18 12:59 PM, Paul Backus wrote:
On Tuesday, 10 April 2018 at 12:34:07 UTC, aliak wrote:
Awesome!
this is a neat trick:
union
{
AliasSeq!(T0, T1) values;
}
Is that usage documented somewhere, or is it somewhere in phobos maybe?
Also, can Algebraic be fully replaced with this version then or is
there some functionality that would stop it going through?
It's called "type sequence instantiation", and it's documented in the
"Compile-time Sequences" article [1] on dlang.org. I discovered it
reading the source of the 'tagged_union' dub package [2]. It's not
mentioned anywhere in the language spec, as far as I can tell.
Ooh! that's really cool.
I've put AliasSeq of types into a struct, but never considered putting
it into a union. This has a lot of potential when you want to
auto-generate unions.
Nice trick!
-Steve
Re: Is std.variant.visit not @nogc?
On Tuesday, 10 April 2018 at 12:34:07 UTC, aliak wrote:
Awesome!
this is a neat trick:
union
{
AliasSeq!(T0, T1) values;
}
Is that usage documented somewhere, or is it somewhere in
phobos maybe?
Also, can Algebraic be fully replaced with this version then or
is there some functionality that would stop it going through?
It's called "type sequence instantiation", and it's documented in
the "Compile-time Sequences" article [1] on dlang.org. I
discovered it reading the source of the 'tagged_union' dub
package [2]. It's not mentioned anywhere in the language spec, as
far as I can tell.
SumType should be capable of doing anything that Algebraic can do
(if it's not, please open an issue on Github!), but it's not a
drop-in replacement, and it's still a work in progress.
Documentation for the current version (more or less) is available
at http://sumtype.dpldocs.info/index.html. If there are any
particular features you'd like to see, let me know, and I'll do
my best to add them.
[1]
https://dlang.org/articles/ctarguments.html#type-seq-instantiation
[2]
https://github.com/Superstar64/tagged_union/blob/master/source/tagged_union.d
Re: Is std.variant.visit not @nogc?
On Tuesday, 10 April 2018 at 03:48:25 UTC, Paul Backus wrote:
Nope! It's just a tagged union, almost exactly the same as what
you'd write by hand in C. You can take a look at the source
yourself, if you're curious---it's actually pretty simple:
https://github.com/pbackus/sumtype/blob/master/src/sumtype.d#L27
Awesome!
this is a neat trick:
union
{
AliasSeq!(T0, T1) values;
}
Is that usage documented somewhere, or is it somewhere in phobos
maybe?
Also, can Algebraic be fully replaced with this version then or
is there some functionality that would stop it going through?
Re: Is std.variant.visit not @nogc?
On Tuesday, 10 April 2018 at 00:22:18 UTC, helxi wrote: On Monday, 9 April 2018 at 15:59:32 UTC, Paul Backus wrote: On Monday, 9 April 2018 at 07:07:58 UTC, Chris Katko wrote: [...] I agree in general, but in this case it's actually completely doable. In fact, I've done it myself: check out 'sumtype' on code.dlang.org. You can replace 'Algebraic' with 'SumType' and 'visit' with 'match' in helxi's example, and everything Just Works™: [...] This isn't boxed by any chance, is it? Nope! It's just a tagged union, almost exactly the same as what you'd write by hand in C. You can take a look at the source yourself, if you're curious---it's actually pretty simple: https://github.com/pbackus/sumtype/blob/master/src/sumtype.d#L27
Re: Is std.variant.visit not @nogc?
On Monday, 9 April 2018 at 15:59:32 UTC, Paul Backus wrote: On Monday, 9 April 2018 at 07:07:58 UTC, Chris Katko wrote: [...] I agree in general, but in this case it's actually completely doable. In fact, I've done it myself: check out 'sumtype' on code.dlang.org. You can replace 'Algebraic' with 'SumType' and 'visit' with 'match' in helxi's example, and everything Just Works™: [...] This isn't boxed by any chance, is it?
Re: Is std.variant.visit not @nogc?
On Monday, 9 April 2018 at 07:07:58 UTC, Chris Katko wrote:
On Monday, 9 April 2018 at 07:02:50 UTC, Hasen Judy wrote:
IMO, this is one more reason why sum-types should be built
into the language compiler, instead of being implemented in
user-space.
+1. Any time you have to "create" a fundamental feature in a
language... from inside the language itself... you're going to
have confusing error messages, and a huge uphill battle.
I agree in general, but in this case it's actually completely
doable. In fact, I've done it myself: check out 'sumtype' on
code.dlang.org. You can replace 'Algebraic' with 'SumType' and
'visit' with 'match' in helxi's example, and everything Just
Works™:
import sumtype;
import core.stdc.stdio;
SumType!(T, string) fib_nth(T)(T n)
{
return n % 15
? n % 5
? n % 3
? SumType!(T, string)(n)
: SumType!(T, string)("Fizz")
: SumType!(T, string)("Buzz")
: SumType!(T, string)("Fizzbuzz");
}
void main() @nogc
{
foreach (i; 1 .. 101)
{
fib_nth(i).match!(
(string s) => printf("%s\n", s.ptr),
(int n) => printf("%i\n", n)
);
}
}
Re: Is std.variant.visit not @nogc?
On Monday, 9 April 2018 at 03:20:58 UTC, helxi wrote:
Is std.variant.visit not @nogc?
These error messages REALLY need to be fixed.
visit, being a template, is @nogc or not based on the arguments
passed to it as well as its own body, so while the error messages
point to visit itself, these are frequently actually caused the
predicate your pass.
well, in this case, it is actually visit itself.
phobos/std/variant.d(2464): Error: @nogc function
std.variant.visitImpl!(true, VariantN!(8u, int, string), function
(string s) => printf("%s\x0a", cast(immutable(char)*)s), function
(int n) => printf("%i\x0a", n)).visitImpl cannot call non-@nogc
constructor std.variant.VariantException.this
phobos/std/variant.d(2469): Error: @nogc function
std.variant.visitImpl!(true, VariantN!(8u, int, string), function
(string s) => printf("%s\x0a", cast(immutable(char)*)s), function
(int n) => printf("%i\x0a", n)).visitImpl cannot call non-@nogc
function std.variant.VariantN!(8u, int,
string).VariantN.peek!int.peek
phobos/std/variant.d(2469): Error: @nogc function
std.variant.visitImpl!(true, VariantN!(8u, int, string), function
(string s) => printf("%s\x0a", cast(immutable(char)*)s), function
(int n) => printf("%i\x0a", n)).visitImpl cannot call non-@nogc
function std.variant.VariantN!(8u, int,
string).VariantN.peek!string.peek
phobos/std/variant.d(2173): Error: template instance
`std.variant.visitImpl!(true, VariantN!(8u, int, string),
function (string s) => printf("%s\x0a", cast(immutable(char)*)s),
function (int n) => printf("%i\x0a", n))` error instantiating
Ugh, so unreadable even on this level, but at least the actual
information is there:
std.variant.VariantException.this is not marked @nogc (but it
prolly could be)
VariantN.peek is not @nogc because it calls Object.opEquals...
which is broken af, sadly, but can probably be fixed for this
case by marking TypeInfo.opEquals nogc.
I think the peek one is going to be the harder one to work around
since any reimplementation of peek is probably going to still
call it... though MAYBE you can use `!is` instead of `!=`... and
any reimplementation of visit needs to check types.
But if you wanna try to work around it, I would copy the
visitImpl and visit functions out of std.variant and do some
adjustments, then call your version instead (which will be fairly
easy btw since they are already UFCS).
FYI: the way I got these error messages was to go into the Phobos
source and add @nogc to the lowest level template in the
instantiation chain. Then just recompile your program - no need
to recompile Phobos itself since they are templates.
I wish the error messages would just do this for you (simulate
@nogc at the second-highest level) to keep you from having to
edit it yourself just to know what it is.
Is std.variant.visit not @nogc?
import std.variant, core.stdc.stdio;
Algebraic!(T, string) fib_nth(T)(T n)
{
return n % 15
? n % 5
? n % 3
? Algebraic!(T, string)(n)
: Algebraic!(T, string)("Fizz")
: Algebraic!(T, string)("Buzz")
: Algebraic!(T, string)("Fizzbuzz");
}
void main() @nogc
{
foreach (i; 1 .. 101)
{
fib_nth(i).visit!(
(string s) => printf("%s\n", s.ptr),
(int n) => printf("%i\n", n)
);
}
}
Complains source/app.d(18,19): Error: @nogc function D main
cannot call non-@nogc function std.variant.visit!(function
(string s) => printf("%s\x0a", cast(immutable(char)*)s), function
(int n) => printf("%i\x0a", n)).visit!(VariantN!(16LU, int,
string)).visit
/usr/bin/dmd failed with exit code 1.
If so, is there a way to emulate `visit` in a @nogc setting?
