Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote:
http://wiki.dlang.org/DIP42
Reading through this thread, I already foresee a messy
specification coming along for this. Instead, I'd propose
something different that would keep the rules consistent yet have
many more applications:
template(...) declaration = ... ;
So what you would have instead:
template(T) enum E = ... ;
template(T) alias A = ... ;
There's also the possibility for simple template constraints as
well:
template(T) if(...) enum E = ... ;
Anything more complicated, such as static if, is probably best
left to the classic style:
template E(T)
{
static if(...) enum E = ... ;
else enum E = ... ;
}
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 06/26/2013 12:15 AM, bearophile wrote: But it's not immediate to assign a generic lambda: alias sum = (x, y) = x + y; Bye, bearophile http://d.puremagic.com/issues/show_bug.cgi?id=9426
Re: DIP42 - Add enum E(T) = expression; eponymous template support
Posted pull request: https://github.com/D-Programming-Language/dmd/pull/2368 Kenji Hara 2013/6/26 Walter Bright newshou...@digitalmars.com http://wiki.dlang.org/DIP42
Re: DIP42 - Add enum E(T) = expression; eponymous template support
Kenji Hara: Posted pull request: https://github.com/D-Programming-Language/dmd/pull/2368 Is implementing that better than implementing issue 7364? Bye, bearophile
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Wednesday, 26 June 2013 at 00:47:53 UTC, Manu wrote: This raises the parallel question of: alias A(T) = expression; Which I think is equally common as the enum case described here? Common or not, I'd expect consistency.
Re: DIP42 - Add enum E(T) = expression; eponymous template support
26.06.2013 20:35, Andrej Mitrovic пишет: On 6/26/13, Denis Shelomovskij verylonglogin@gmail.com wrote: which will look better this way: --- static if (...) enum template = ...; else static if (...) enum template = ...; else ... --- Yeah I agree, this is more important than DIP42's shortened syntax for simple templates. It's the more complicated templates that are the problem. It's rather strange that enhancement 7364 isn't implemented yet (and even not discussed) as it's an easy-to-implement change with big pros and no cons. -- Денис В. Шеломовский Denis V. Shelomovskij
Re: DIP42 - Add enum E(T) = expression; eponymous template support
I've been wondering if we could have parameterized named enumS.
The syntax for it would look somewhat similar:
enum Fruit(T) : T { apple, banana = -42 }
void main()
{
auto shortFruit = Fruit!(short).apple;
auto longFruit = Fruit!(long).banana;
longFruit = shortFruit; // OK: implicit conversion allowed
shortFruit = longFruit; // OK: ... even a truncating one
Fruit!uint uintFruit; // Error: -42 is out of range of uint
Fruit!string stringFruit; // Error: enums need initializers
}
Re: DIP42 - Add enum E(T) = expression; eponymous template support
26.06.2013 1:31, Walter Bright пишет: http://wiki.dlang.org/DIP42 What about enhancement 7364 [1] (from [2] discussion)? As we still have such cases: --- static if (...) enum fullyQualifiedNameImplForTypes = ...; else static if (...) enum fullyQualifiedNameImplForTypes = ...; else static if (...) ... --- which will look better this way: --- static if (...) enum template = ...; else static if (...) enum template = ...; else ... --- Also note current syntax is error-prone as one can easily make a typo or copy paste mistake which will lead to cryptic template errors. [1] http://d.puremagic.com/issues/show_bug.cgi?id=7364 [2] http://forum.dlang.org/thread/jfh7po$3b$1...@digitalmars.com?page=1 -- Денис В. Шеломовский Denis V. Shelomovskij
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 6/26/13, Denis Shelomovskij verylonglogin@gmail.com wrote: which will look better this way: --- static if (...) enum template = ...; else static if (...) enum template = ...; else ... --- Yeah I agree, this is more important than DIP42's shortened syntax for simple templates. It's the more complicated templates that are the problem.
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 06/25/2013 11:31 PM, Walter Bright wrote: http://wiki.dlang.org/DIP42 The answer to life, the universe and everything? :-)
DIP42 - Add enum E(T) = expression; eponymous template support
http://wiki.dlang.org/DIP42
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote: http://wiki.dlang.org/DIP42 I suppose the alias version will work too? IOW: alias Select(size_t idx, T...) = T[idx]; static assert(is(Select!(0, int, float) == int)); static assert(is(Select!(1, int, float) == float));
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 6/25/2013 2:33 PM, Andrej Mitrovic wrote: On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote: http://wiki.dlang.org/DIP42 I suppose the alias version will work too? IOW: alias Select(size_t idx, T...) = T[idx]; static assert(is(Select!(0, int, float) == int)); static assert(is(Select!(1, int, float) == float)); That's something separate.
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 06/25/2013 11:31 PM, Walter Bright wrote: http://wiki.dlang.org/DIP42 enum syntactically is a storage class. Will this be special syntax initiated by enum ident ( or work whenever enum is within the specified storage classes?
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 6/25/2013 3:00 PM, Timon Gehr wrote: On 06/25/2013 11:31 PM, Walter Bright wrote: http://wiki.dlang.org/DIP42 enum syntactically is a storage class. Will this be special syntax initiated by enum ident ( Yes. or work whenever enum is within the specified storage classes? No.
Re: DIP42 - Add enum E(T) = expression; eponymous template support
Walter Bright:
http://wiki.dlang.org/DIP42
I like it, it feels natural (probably other persons have invented
the same idea).
In C++14 they wish to add generic lambdas:
http://en.wikipedia.org/wiki/C%2B%2B14#Generic_lambdas
Like:
auto lambda = [](auto x, auto y) {return x + y;}
In D we use generic lambdas often:
import std.stdio, std.algorithm;
void main() {
[1, 2, 3].reduce!((x, y) = x + y).writeln;
}
But it's not immediate to assign a generic lambda:
alias sum = (x, y) = x + y;
Bye,
bearophile
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Tuesday, June 25, 2013 14:31:14 Walter Bright wrote: http://wiki.dlang.org/DIP42 It seems simple enough to me. I don't have a problem with it. By the way, I don't know how much it matters, but there's no author on the DIP like there normally is (I assume that it's you, but it doesn't say). - Jonathan M Davis
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On 6/25/2013 3:19 PM, Jonathan M Davis wrote: By the way, I don't know how much it matters, but there's no author on the DIP like there normally is (I assume that it's you, but it doesn't say). The D-9000 computer did it. (That huge data center being built in Iowa is really a giant extension to D-9000's neural centers. Be afraid! D-9000 will soon be everywhere!)
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote: http://wiki.dlang.org/DIP42 The proposal doesn't include suggested changes to the language grammar specification. On the other hand, neither did user defined attributes or the syntax for passing messages to deprecated statements, so there's certainly precedent for doing this.
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Wednesday, June 26, 2013 01:09:26 Brian Schott wrote: On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote: http://wiki.dlang.org/DIP42 The proposal doesn't include suggested changes to the language grammar specification. On the other hand, neither did user defined attributes or the syntax for passing messages to deprecated statements, so there's certainly precedent for doing this. Not that it's a bad idea to show how a proposed change would affect the grammar, but I'm not aware of _any_ proposed language change where the effects on the grammar were ever shown. I'm not sure that they've ever really even been discussed as part of assessing possible language changes. If they were, it was merely to show that the proposal was ambiguous rather than to try and discuss how the grammar should be changed in order to add the proposed feature. - Jonathan M Davis
Re: DIP42 - Add enum E(T) = expression; eponymous template support
On Tue, 25 Jun 2013 19:09:26 -0400, Brian Schott briancsch...@gmail.com wrote: On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote: http://wiki.dlang.org/DIP42 The proposal doesn't include suggested changes to the language grammar specification. Considering the state of the grammar, I don't know if it is critical for the process. BUT, I would suggest we should include grammar proposals with language proposals. Especially from the language author. -Steve
Re: DIP42 - Add enum E(T) = expression; eponymous template support
This raises the parallel question of: alias A(T) = expression; Which I think is equally common as the enum case described here? On 26 June 2013 07:31, Walter Bright newshou...@digitalmars.com wrote: http://wiki.dlang.org/DIP42
Re: DIP42 - Add enum E(T) = expression; eponymous template support
2013/6/26 Walter Bright newshou...@digitalmars.com On 6/25/2013 2:33 PM, Andrej Mitrovic wrote: On Tuesday, 25 June 2013 at 21:31:15 UTC, Walter Bright wrote: http://wiki.dlang.org/DIP42 I suppose the alias version will work too? IOW: alias Select(size_t idx, T...) = T[idx]; static assert(is(Select!(0, int, float) == int)); static assert(is(Select!(1, int, float) == float)); That's something separate. I don't think so. DIP42 should consider alias version, from the grammatical view. enum basically takes an expression, enum E(T) = expression; But alias should take a type grammatically. alias A(T) = type; And one more question: How template constraint will be written? enum E(T) if (isSomething!T) = expression; // is this supposed? Kenji Hara
