www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Alias/Ref Tuples ?

reply Joshua Reusch <yoschi arkandos.de> writes:
Hello,

is there a way to say something like

---
int a, b;
AliasTuple!(a, b) = tuple(4,5);
assert(a == 4 && b == 5);
---

without having to write an own AliasTuple template ? I want to use it 
for functions returning multiple values.

Joshua Reusch
Dec 16 2011
next sibling parent Trass3r <un known.com> writes:
I think something like this is implemented in a dmd pull request.
Dec 16 2011
prev sibling next sibling parent Joshua Reusch <yoschi arkandos.de> writes:
I found a way doing this with a simple function:

---
void explode(R, T...)(R range, ref T values) {
	static if(hasLength!R) assert(range.length == T.length);
	foreach(i, value; range) values[i] = value;
}
---

but a more self-documenting version would be nice.
Dec 16 2011
prev sibling next sibling parent reply =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Fri, 16 Dec 2011 14:00:11 +0100, Joshua Reusch <yoschi arkandos.de>  
wrote:


 Hello,

 is there a way to say something like

 ---
 int a, b;
 AliasTuple!(a, b) = tuple(4,5);
 assert(a == 4 && b == 5);
 ---

 without having to write an own AliasTuple template ? I want to use it  
 for functions returning multiple values.


There is one in dranges:

http://dsource.org/projects/dranges

It is not officially documented, and I don't know how good it actually is,
but here's what documentation exists:

http://svn.dsource.org/projects/dranges/trunk/dranges/docs/reftuple.html
Dec 16 2011
parent Philippe Sigaud <philippe.sigaud gmail.com> writes:
 There is one in dranges:

 http://dsource.org/projects/dranges

 It is not officially documented, and I don't know how good it actually is,
 but here's what documentation exists:

 http://svn.dsource.org/projects/dranges/trunk/dranges/docs/reftuple.html


Hmm, thanks Simen, but no. It was a simple hack I did in 10' one day
to play with pointers without knowing what I was doing. I wouldn't use
it if I were you, it's quite unsafe.

I'm following with *great* interest all the nice changes in DMD that
Kanji is adding.  We may have a nice tuple syntax in 2012, who knows?
Gosh, there should be a way to get extensions into DMD, like the
Glasgow Haskell Compiler. Like:

pragma(extension, tupleExpansionSyntax); // thanks, Kanji!


Philippe
Dec 16 2011
prev sibling parent reply =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Fri, 16 Dec 2011 14:00:11 +0100, Joshua Reusch <yoschi arkandos.de>  
wrote:


 Hello,

 is there a way to say something like

 ---
 int a, b;
 AliasTuple!(a, b) = tuple(4,5);
 assert(a == 4 && b == 5);
 ---

 without having to write an own AliasTuple template ? I want to use it  
 for functions returning multiple values.


A few small tests later:

import std.typetuple;
import std.typecons;
import std.stdio;

void main() {
     int a, b;
     TypeTuple!(a, b) = tuple(4,5);
     assert(a == 4 && b == 5);
}

In other words, the language already has this.

Note that TypeTuple!(a,b) = TypeTuple!(b,a) also works, but sets both a  
and b equal to b.
Dec 16 2011
next sibling parent Joshua Reusch <yoschi arkandos.de> writes:
Am 17.12.2011 01:23, schrieb Simen Kjærås:

 On Fri, 16 Dec 2011 14:00:11 +0100, Joshua Reusch <yoschi arkandos.de>
 wrote:


 Hello,

 is there a way to say something like

 ---
 int a, b;
 AliasTuple!(a, b) = tuple(4,5);
 assert(a == 4 && b == 5);
 ---

 without having to write an own AliasTuple template ? I want to use it
 for functions returning multiple values.


 A few small tests later:

 import std.typetuple;
 import std.typecons;
 import std.stdio;

 void main() {
 int a, b;
 TypeTuple!(a, b) = tuple(4,5);
 assert(a == 4 && b == 5);
 }

 In other words, the language already has this.

 Note that TypeTuple!(a,b) = TypeTuple!(b,a) also works, but sets both a
 and b equal to b.


Thank you ! This is exactly what I needed ! I didnt thought TypeTuple 
can do this.
Dec 16 2011
prev sibling parent Philippe Sigaud <philippe.sigaud gmail.com> writes:
On Sat, Dec 17, 2011 at 01:23, Simen Kj=C3=A6r=C3=A5s <simen.kjaras gmail.c=
om> wrote:

 A few small tests later:

 import std.typetuple;
 import std.typecons;
 import std.stdio;

 void main() {
 =C2=A0 =C2=A0int a, b;
 =C2=A0 =C2=A0TypeTuple!(a, b) =3D tuple(4,5);

 =C2=A0 =C2=A0assert(a =3D=3D 4 && b =3D=3D 5);
 }

 In other words, the language already has this.


Wow. How does that work?  I'd understand:

TypeTuple!(a,b) =3D tuple(a,b).expand; // Or .tupleof, even.

but not your example... Does that mean TypeTuple!() =3D does some destructu=
ring?

Let's do some test:

struct Pair1 { TypeTuple!(int,int) value; }
struct Pair2 { TypeTuple!(int,int) value; alias value this;}

void main() {

    int a, b;
    a =3D 1;
    b =3D 2;

//  TypeTuple!(a, b) =3D Pair1(b, a+b); // boom!
    TypeTuple!(a, b) =3D Pair2(b, a+b); // works!
    writeln(a," ",b);
}

So it's a side effect of alias this and tuples...
Dec 17 2011