Re: [Request] A way to extract all instance of X from a range
On Monday, 21 March 2016 at 11:34:15 UTC, Nick Treleaven wrote: There is a pull for Option: https://github.com/D-Programming-Language/phobos/pull/3915 We could have: // fun takes r.front and produces an Option of that type auto mapFilter(alias fun, R)(R r); // turn a possibly null value into an Option Option!T nullFilter(T)(T v) if (isNullable!T); auto src = [new Object(), new T(), null]; auto res = mapFilter!(e => nullFilter(cast(T)e)); assert(res.equal([src[1]])); Using the interface proposed in the PR: auto src = [new Object(), new T(), null]; assert(src.map!(e => option(cast(T)e)).joiner.equal(only(src[1])));
Re: [Request] A way to extract all instance of X from a range
On Wednesday, 23 March 2016 at 11:36:39 UTC, Nick Treleaven wrote: On Tuesday, 22 March 2016 at 20:09:51 UTC, Matthias Bentrup wrote: It is logically just a combination of map and concat (which turns a range of ranges into a combined range, but I think that one is missing in the std lib too). http://dlang.org/phobos/std_range.html#.chain Or joiner(), if you have a range of ranges: http://dlang.org/phobos/std_algorithm_iteration.html#.joiner
Re: [Request] A way to extract all instance of X from a range
On Tuesday, 22 March 2016 at 20:09:51 UTC, Matthias Bentrup wrote: It is logically just a combination of map and concat (which turns a range of ranges into a combined range, but I think that one is missing in the std lib too). http://dlang.org/phobos/std_range.html#.chain
Re: [Request] A way to extract all instance of X from a range
On Monday, 21 March 2016 at 11:50:06 UTC, Timothee Cour wrote:
On Mon, Mar 21, 2016 at 4:34 AM, Nick Treleaven via
Digitalmars-d < digitalmars-d@puremagic.com> wrote:
On 14/03/2016 11:32, thedeemon wrote:
filter_map : ('a -> 'b option) -> 'a t -> 'b t
"filter_map f e returns an enumeration over all elements x
such as f y returns Some x, where y is an element of e."
It is really convenient and comes handy in many situations.
However it requires some common Option/Maybe type that
different libraries could use.
There is a pull for Option:
https://github.com/D-Programming-Language/phobos/pull/3915
We could have:
// fun takes r.front and produces an Option of that type
auto mapFilter(alias fun, R)(R r);
// turn a possibly null value into an Option
Option!T nullFilter(T)(T v) if (isNullable!T);
auto src = [new Object(), new T(), null];
auto res = mapFilter!(e => nullFilter(cast(T)e));
assert(res.equal([src[1]]));
see my proposal [+implementation] for emit
http://forum.dlang.org/post/mailman.538.1458560190.26339.digitalmar...@puremagic.com
emit is more powerfull, and generalizes map,filter,joiner
auto res = src.mapFilter!(e=>nullFilter(cast(T)e));
with emit:
auto res = src.emit!((put,e){if(cast(T)e) put(e);});
Why don't you go for the well-established monadic bind function ?
A rangified bind would take a range of inputs, a lambda returning
a range of results for one input and return a range of all
results.
It is logically just a combination of map and concat (which turns
a range of ranges into a combined range, but I think that one is
missing in the std lib too).
Re: [Request] A way to extract all instance of X from a range
On Mon, Mar 21, 2016 at 4:34 AM, Nick Treleaven via Digitalmars-d <
digitalmars-d@puremagic.com> wrote:
> On 14/03/2016 11:32, thedeemon wrote:
>
>>
>> filter_map : ('a -> 'b option) -> 'a t -> 'b t
>>
>> "filter_map f e returns an enumeration over all elements x such as f y
>> returns Some x, where y is an element of e."
>>
>> It is really convenient and comes handy in many situations. However it
>> requires some common Option/Maybe type that different libraries could use.
>>
>
> There is a pull for Option:
> https://github.com/D-Programming-Language/phobos/pull/3915
>
> We could have:
>
> // fun takes r.front and produces an Option of that type
> auto mapFilter(alias fun, R)(R r);
>
> // turn a possibly null value into an Option
> Option!T nullFilter(T)(T v) if (isNullable!T);
>
> auto src = [new Object(), new T(), null];
> auto res = mapFilter!(e => nullFilter(cast(T)e));
> assert(res.equal([src[1]]));
>
>
>
see my proposal [+implementation] for emit
http://forum.dlang.org/post/mailman.538.1458560190.26339.digitalmar...@puremagic.com
emit is more powerfull, and generalizes map,filter,joiner
auto res = src.mapFilter!(e=>nullFilter(cast(T)e));
with emit:
auto res = src.emit!((put,e){if(cast(T)e) put(e);});
Re: [Request] A way to extract all instance of X from a range
On 14/03/2016 11:32, thedeemon wrote:
filter_map : ('a -> 'b option) -> 'a t -> 'b t
"filter_map f e returns an enumeration over all elements x such as f y
returns Some x, where y is an element of e."
It is really convenient and comes handy in many situations. However it
requires some common Option/Maybe type that different libraries could use.
There is a pull for Option:
https://github.com/D-Programming-Language/phobos/pull/3915
We could have:
// fun takes r.front and produces an Option of that type
auto mapFilter(alias fun, R)(R r);
// turn a possibly null value into an Option
Option!T nullFilter(T)(T v) if (isNullable!T);
auto src = [new Object(), new T(), null];
auto res = mapFilter!(e => nullFilter(cast(T)e));
assert(res.equal([src[1]]));
Re: [Request] A way to extract all instance of X from a range
On Tuesday, 15 March 2016 at 07:42:58 UTC, Stefan Koch wrote:
On Tuesday, 15 March 2016 at 04:05:11 UTC, Meta wrote:
I believe this should work with the latest DMD:
alias castRange(T) = t => t.map!(x => cast(T) x).filter!(x =>
x !is null);
No it does not.
However this works :
auto typeFilter(T, Range)(Range range) {
import std.algorithm : filter, map;
import std.traits : ForeachType;
static assert(is(T == class) && is(T : ForeachType!Range),
"typeFilter only works with classes that are derived form
each other");
return range.map!(x => cast(T) x).filter!(x => x !is null);
}
You're Welcome.
What version of DMD are you using? It compiles and a small test
works for me on 2.070.2.
Re: [Request] A way to extract all instance of X from a range
On Tuesday, 15 March 2016 at 04:05:11 UTC, Meta wrote:
I believe this should work with the latest DMD:
alias castRange(T) = t => t.map!(x => cast(T) x).filter!(x => x
!is null);
No it does not.
However this works :
auto typeFilter(T, Range)(Range range) {
import std.algorithm : filter, map;
import std.traits : ForeachType;
static assert(is(T == class) && is(T : ForeachType!Range),
"typeFilter only works with classes that are derived form each
other");
return range.map!(x => cast(T) x).filter!(x => x !is null);
}
You're Welcome.
Re: [Request] A way to extract all instance of X from a range
On Monday, 14 March 2016 at 23:34:37 UTC, Stefan Koch wrote: On Monday, 14 March 2016 at 08:04:18 UTC, deadalnix wrote: Right now, I'm repeating the following pattern many times : range.map!(x => cast(Foo) x).filter!(x => x !is null) Which is kind of annoying. Could we get something in phobos to do this ? There you go ;) alias castRange(T) = map!(x => cast(T) x).filter!(x => x !is null); I believe this should work with the latest DMD: alias castRange(T) = t => t.map!(x => cast(T) x).filter!(x => x !is null);
Re: [Request] A way to extract all instance of X from a range
On Monday, 14 March 2016 at 23:34:37 UTC, Stefan Koch wrote: On Monday, 14 March 2016 at 08:04:18 UTC, deadalnix wrote: Right now, I'm repeating the following pattern many times : range.map!(x => cast(Foo) x).filter!(x => x !is null) Which is kind of annoying. Could we get something in phobos to do this ? There you go ;) alias castRange(T) = map!(x => cast(T) x).filter!(x => x !is null); Ooops ;) didn't work then it'll has to be done with a wrapper struct ...
Re: [Request] A way to extract all instance of X from a range
On Monday, 14 March 2016 at 08:04:18 UTC, deadalnix wrote: Right now, I'm repeating the following pattern many times : range.map!(x => cast(Foo) x).filter!(x => x !is null) Which is kind of annoying. Could we get something in phobos to do this ? There you go ;) alias castRange(T) = map!(x => cast(T) x).filter!(x => x !is null);
Re: [Request] A way to extract all instance of X from a range
On Monday, 14 March 2016 at 08:04:18 UTC, deadalnix wrote: Right now, I'm repeating the following pattern many times : range.map!(x => cast(Foo) x).filter!(x => x !is null) Which is kind of annoying. Could we get something in phobos to do this ? you could use an alias. alias NullFliter = filter!(x => x !is null);
Re: [Request] A way to extract all instance of X from a range
On Monday, 14 March 2016 at 08:04:18 UTC, deadalnix wrote:
Right now, I'm repeating the following pattern many times :
range.map!(x => cast(Foo) x).filter!(x => x !is null)
This reminds me of a function in OCaml extended stdlib that I've
used quite often and really miss in D:
filter_map : ('a -> 'b option) -> 'a list -> 'b list
"filter_map f l call (f a0) (f a1) (f an) where a0..an are
the elements of l. It returns the list of elements bi such as f
ai = Some bi (when f returns None, the corresponding element of l
is discarded)."
Or its variant for OCaml's analog of ranges:
filter_map : ('a -> 'b option) -> 'a t -> 'b t
"filter_map f e returns an enumeration over all elements x such
as f y returns Some x, where y is an element of e."
It is really convenient and comes handy in many situations.
However it requires some common Option/Maybe type that different
libraries could use.
Re: [Request] A way to extract all instance of X from a range
On Monday, 14 March 2016 at 08:04:18 UTC, deadalnix wrote: Right now, I'm repeating the following pattern many times : range.map!(x => cast(Foo) x).filter!(x => x !is null) Which is kind of annoying. Could we get something in phobos to do this ? BTW, .NET has an extension method called OfType that does the same thing: https://msdn.microsoft.com/library/bb360913(v=vs.100).aspx which is different from Cast, which throws an exception if an element can't be converted: https://msdn.microsoft.com/library/bb341406(v=vs.100).aspx How do you want to handle this? With two separate methods as in .NET, or with a template parameter? Maybe something like this: /// Returns a range that lazily iterates over /// the elements in `source` and converts each /// of them to type `T`. /// /// If `throwOnConvError` is false, elements /// that can't be converted will be skipped. auto ofType (T, bool throwOnConvError = true, Range) (Range source) if (isInputRange!Range)
[Request] A way to extract all instance of X from a range
Right now, I'm repeating the following pattern many times : range.map!(x => cast(Foo) x).filter!(x => x !is null) Which is kind of annoying. Could we get something in phobos to do this ?
