www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Runtime heterogeneous collections?

reply Steven O <oliver.steven gmail.com> writes:
I want to create a heterogeneous collection of red-black trees, 
and I can't seem to figure out if it's possible.

I can easily do:

import std.container.rbtree;
import std.typecons;

void main()
{
     alias Rec_type = Tuple!(int, "x", int, "y", int, "z");
     RedBlackTree!Rec_type[1] test;
}

That works great, but I can only add red-black trees of Rec_type. 
What if I want the collection of red-black trees to be different? 
So if you printed out the collection of red-black trees you'd see 
something akin to:

// Formatted for easier reading
[
  RedBlackTree([Tuple!(int, "x", int, "y", string, "z")(1, 2, 
"abc")]),
  RedBlackTree([Tuple!(int, "x", int, "y", int, "z")(1, 2, 3)])
]

Is it possible to do this?
Jan 16
next sibling parent reply Neia Neutuladh <neia ikeran.org> writes:
On Thu, 17 Jan 2019 02:21:21 +0000, Steven O wrote:
 I want to create a heterogeneous collection of red-black trees, and I
 can't seem to figure out if it's possible.
RedBlackTree!int and RedBlackTree!string are entirely different types (they just happen to be generated from the same template). There are two reasonable ways of doing things: 1. Make a wrapper class. Now you can store Object[], or you can make a base class or base interface and use that. 2. Use Variant, which can wrap anything, or the related Algebraic, which can wrap a fixed collection of types. You can use this technique either with the collection types themselves or with the value types.
Jan 16
next sibling parent reply Dukc <ajieskola gmail.com> writes:
On Thursday, 17 January 2019 at 02:27:20 UTC, Neia Neutuladh 
wrote:
 1. Make a wrapper class. Now you can store Object[], or you can 
 make a
 base class or base interface and use that.
 2. Use Variant, which can wrap anything, or the related 
 Algebraic, which
 can wrap a fixed collection of types.
3. Use an union. However, only do this if you always know from outside what type of data is stored in each node. If you need to memoize the type of data for each node, better resort to 1. or 2.
Jan 17
parent reply Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Thursday, January 17, 2019 1:21:41 AM MST Dukc via Digitalmars-d-learn 
wrote:
 On Thursday, 17 January 2019 at 02:27:20 UTC, Neia Neutuladh

 wrote:
 1. Make a wrapper class. Now you can store Object[], or you can
 make a
 base class or base interface and use that.
 2. Use Variant, which can wrap anything, or the related
 Algebraic, which
 can wrap a fixed collection of types.
3. Use an union. However, only do this if you always know from outside what type of data is stored in each node. If you need to memoize the type of data for each node, better resort to 1. or 2.
Variant types are really just user-friendly wrappers around unions. So, pedantically, using a variant type such as Variant or Albegbraic and using a union are fundamentally the same thing, though obviously, the actual usage in terms of the code that you write is not the same, since if you use a union directly, you have to deal with the union directly (including figuring out how to know which type the union currently holds), whereas with a Variant, you're using its API rather than dealing with the union directly. In general, it's probably better to use Variant rather than union simply because Variant deals with the type safety for you. - Jonathan M Davis
Jan 17
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 1/17/19 11:06 PM, Jonathan M Davis wrote:
 On Thursday, January 17, 2019 1:21:41 AM MST Dukc via Digitalmars-d-learn
 wrote:
 On Thursday, 17 January 2019 at 02:27:20 UTC, Neia Neutuladh

 wrote:
 1. Make a wrapper class. Now you can store Object[], or you can
 make a
 base class or base interface and use that.
 2. Use Variant, which can wrap anything, or the related
 Algebraic, which
 can wrap a fixed collection of types.
3. Use an union. However, only do this if you always know from outside what type of data is stored in each node. If you need to memoize the type of data for each node, better resort to 1. or 2.
Variant types are really just user-friendly wrappers around unions. So, pedantically, using a variant type such as Variant or Albegbraic and using a union are fundamentally the same thing, though obviously, the actual usage in terms of the code that you write is not the same, since if you use a union directly, you have to deal with the union directly (including figuring out how to know which type the union currently holds), whereas with a Variant, you're using its API rather than dealing with the union directly. In general, it's probably better to use Variant rather than union simply because Variant deals with the type safety for you.
A variant is not a union. Algebraic is a union, but Variant can hold ANY type, even types your code doesn't know about. To answer the OP, what he wants is an array of different RedBlackTrees. Since RedBlackTree is a class, his code is not far off from something that works. This does compile, and produces an Object[]: auto arr = [ redBlackTree(Tuple!(int, "x", int, "y", string, "z")(1, 2, "abc")), redBlackTree(Tuple!(int, "x", int, "y", int, "z")(1, 2, 3)) ]; Then you have to cast each object into it's appropriate type to use it. That is not as easy, as you have to know the exact instantiation of tree type. In this case, you are better off using a union, or an Algebraic as your array element type. If you use something like https://code.dlang.org/packages/taggedalgebraic it could be quite usable. -Steve
Jan 18
parent reply Alex <sascha.orlov gmail.com> writes:
On Friday, 18 January 2019 at 13:31:28 UTC, Steven Schveighoffer 
wrote:
 To answer the OP, what he wants is an array of different 
 RedBlackTrees. Since RedBlackTree is a class, his code is not 
 far off from something that works. This does compile, and 
 produces an Object[]:

     auto arr = [
  redBlackTree(Tuple!(int, "x", int, "y", string, "z")(1, 2, 
 "abc")),
  redBlackTree(Tuple!(int, "x", int, "y", int, "z")(1, 2, 3))
 ];

 Then you have to cast each object into it's appropriate type to 
 use it. That is not as easy, as you have to know the exact 
 instantiation of tree type.
In this case, I would say Phobos lacks an appropriate interface definition, what do you think?
Jan 18
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 1/18/19 9:58 AM, Alex wrote:
 On Friday, 18 January 2019 at 13:31:28 UTC, Steven Schveighoffer wrote:
 To answer the OP, what he wants is an array of different 
 RedBlackTrees. Since RedBlackTree is a class, his code is not far off 
 from something that works. This does compile, and produces an Object[]:

     auto arr = [
  redBlackTree(Tuple!(int, "x", int, "y", string, "z")(1, 2, "abc")),
  redBlackTree(Tuple!(int, "x", int, "y", int, "z")(1, 2, 3))
 ];

 Then you have to cast each object into it's appropriate type to use 
 it. That is not as easy, as you have to know the exact instantiation 
 of tree type.
In this case, I would say Phobos lacks an appropriate interface definition, what do you think?
But what is the common interface between those 2 types? Even in Dcollections, where RedBlackTree came from, there was no interfaces that didn't specify the type they were dealing with. In other words, there is no common interface for sets of 2 different types. -Steve
Jan 18
next sibling parent reply Neia Neutuladh <neia ikeran.org> writes:
On Fri, 18 Jan 2019 10:07:41 -0500, Steven Schveighoffer wrote:
 But what is the common interface between those 2 types? Even in
 Dcollections, where RedBlackTree came from, there was no interfaces that
 didn't specify the type they were dealing with. In other words, there is
 no common interface for sets of 2 different types.
.empty(), .clear(), .length(), and .toString(sink, formatspec). Which is kind of anemic. Might as well use Object.
Jan 18
parent Steven Schveighoffer <schveiguy gmail.com> writes:
On 1/18/19 10:10 AM, Neia Neutuladh wrote:
 On Fri, 18 Jan 2019 10:07:41 -0500, Steven Schveighoffer wrote:
 But what is the common interface between those 2 types? Even in
 Dcollections, where RedBlackTree came from, there was no interfaces that
 didn't specify the type they were dealing with. In other words, there is
 no common interface for sets of 2 different types.
..empty(), .clear(), .length(), and .toString(sink, formatspec). Which is kind of anemic. Might as well use Object.
Yeah, I didn't bother with any of those as base interfaces. Probably the most basic interface for dcollections was Iterator(V): https://github.com/schveiguy/dcollections/blob/master/dcollections/model/Iterator.d#L40-L58 -Steve
Jan 18
prev sibling parent Alex <sascha.orlov gmail.com> writes:
On Friday, 18 January 2019 at 15:07:41 UTC, Steven Schveighoffer 
wrote:
 On 1/18/19 9:58 AM, Alex wrote:
 On Friday, 18 January 2019 at 13:31:28 UTC, Steven 
 Schveighoffer wrote:
[...]
In this case, I would say Phobos lacks an appropriate interface definition, what do you think?
But what is the common interface between those 2 types? Even in Dcollections, where RedBlackTree came from, there was no interfaces that didn't specify the type they were dealing with. In other words, there is no common interface for sets of 2 different types. -Steve
Aha... I see... all important methods are templated on the element type... hmm.
Jan 18
prev sibling parent reply Seb <seb wilzba.ch> writes:
On Thursday, 17 January 2019 at 02:27:20 UTC, Neia Neutuladh 
wrote:
 On Thu, 17 Jan 2019 02:21:21 +0000, Steven O wrote:
 I want to create a heterogeneous collection of red-black 
 trees, and I can't seem to figure out if it's possible.
RedBlackTree!int and RedBlackTree!string are entirely different types (they just happen to be generated from the same template). There are two reasonable ways of doing things: 1. Make a wrapper class. Now you can store Object[], or you can make a base class or base interface and use that. 2. Use Variant, which can wrap anything, or the related Algebraic, which can wrap a fixed collection of types. You can use this technique either with the collection types themselves or with the value types.
As the OP is most likely looking for Variant, let me link to it: https://dlang.org/phobos/std_variant.html#Variant
Jan 17
parent Steven O <oliver.steven gmail.com> writes:
I'd like to thank everyone for their help! I was finally able to 
do what I'd like. I didn't end up using a variant, but maybe 
there's a better way to do what I want using it, and I just 
couldn't figure it out.

Here's the solution I finally came up with:
https://run.dlang.io/is/GdDDBp

If anyone has any better solutions I'm all ears!
Jan 19
prev sibling parent Kagamin <spam here.lot> writes:
On Thursday, 17 January 2019 at 02:21:21 UTC, Steven O wrote:
 void main()
 {
     alias Rec_type = Tuple!(int, "x", int, "y", int, "z");
     RedBlackTree!Rec_type[1] test;
 }
alias Rec_type1 = Tuple!(int, "x", int, "y", int, "z"); alias Rec_type2 = Tuple!(int, "x", int, "y", string, "z"); Tuple!(RedBlackTree!Rec_type1, "x", RedBlackTree!Rec_type2, "z") test; Similar questions were asked before, usually such heterogeneous collections are not the best solution to the problem at hand.
Jan 18