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digitalmars.D.learn - Append to 'map' result

reply Jean-Louis Leroy <jl leroy.nyc> writes:
I want to create a range that consists of the result of a map() 
followed by a value, e.g.:

   int[] x = [ 1, 2, 3];
   auto y = map!(x => x * x)(x);
   auto z = y ~ 99; // how???

I have tried several variations: convert 99 to a dynamic array, 
to a range, convert range to dynamic array (couldn't even figure 
that one); to no avail.

Help please...
Jul 04 2017
next sibling parent reply "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
On Tue, Jul 04, 2017 at 11:27:25PM +0000, Jean-Louis Leroy via
Digitalmars-d-learn wrote:

 I want to create a range that consists of the result of a map()
 followed by a value, e.g.:
 
   int[] x = [ 1, 2, 3];
   auto y = map!(x => x * x)(x);
   auto z = y ~ 99; // how???
 
 I have tried several variations: convert 99 to a dynamic array, to a
 range, convert range to dynamic array (couldn't even figure that one);
 to no avail.


[...]

Try:

	auto z = chain(y, only(99));


T

-- 
I don't trust computers, I've spent too long programming to think that they can
get anything right. -- James Miller
Jul 04 2017
parent reply Jean-Louis Leroy <jl leroy.nyc> writes:
On Tuesday, 4 July 2017 at 23:26:28 UTC, H. S. Teoh wrote:

 On Tue, Jul 04, 2017 at 11:27:25PM +0000, Jean-Louis Leroy via 
 Digitalmars-d-learn wrote:

 I want to create a range that consists of the result of a map()
 followed by a value, e.g.:
 
   int[] x = [ 1, 2, 3];
   auto y = map!(x => x * x)(x);
   auto z = y ~ 99; // how???
 
 I have tried several variations: convert 99 to a dynamic 
 array, to a range, convert range to dynamic array (couldn't 
 even figure that one); to no avail.


 [...]

 Try:

 	auto z = chain(y, only(99));


Thanks!

However, when I try to use this construct in my real code, I 
still have a problem:

     // k is a ClassInfo
     chain(map!(i => i.classinfo)(k.interfaces), only(k.base))

meth.d(311): Error: template std.range.chain cannot deduce 
function from argument types !()(MapResult!(__lambda3, 
Interface[]), OnlyResult!(TypeInfo_Class, 1LU)), candidates are:
/usr/include/d/std/range/package.d(795):        
std.range.chain(Ranges...)(Ranges rs) if (Ranges.length > 0 && 
allSatisfy!(isInputRange, staticMap!(Unqual, Ranges)) && 
!is(CommonType!(staticMap!(ElementType, staticMap!(Unqual, 
Ranges))) == void))
Jul 04 2017
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 07/04/2017 04:57 PM, Jean-Louis Leroy wrote:

 On Tuesday, 4 July 2017 at 23:26:28 UTC, H. S. Teoh wrote:

 On Tue, Jul 04, 2017 at 11:27:25PM +0000, Jean-Louis Leroy via
 Digitalmars-d-learn wrote:

 I want to create a range that consists of the result of a map()
 followed by a value, e.g.:

   int[] x = [ 1, 2, 3];
   auto y = map!(x => x * x)(x);
   auto z = y ~ 99; // how???

 I have tried several variations: convert 99 to a dynamic array, to a
 range, convert range to dynamic array (couldn't even figure that
 one); to no avail.


 [...]

 Try:

     auto z = chain(y, only(99));


 Thanks!

 However, when I try to use this construct in my real code, I still have
 a problem:

     // k is a ClassInfo
     chain(map!(i => i.classinfo)(k.interfaces), only(k.base))

 meth.d(311): Error: template std.range.chain cannot deduce function from
 argument types !()(MapResult!(__lambda3, Interface[]),
 OnlyResult!(TypeInfo_Class, 1LU)), candidates are:
 /usr/include/d/std/range/package.d(795):
 std.range.chain(Ranges...)(Ranges rs) if (Ranges.length > 0 &&
 allSatisfy!(isInputRange, staticMap!(Unqual, Ranges)) &&
 !is(CommonType!(staticMap!(ElementType, staticMap!(Unqual, Ranges))) ==
 void))


No time to dig deeper but this is because the two ranges that chain() 
receives do not have a common type. (Rather, that type is 'void'):

import std.algorithm;
import std.range;
import std.traits;

class C {
}

void main() {
     auto k = C.classinfo;
     auto m = map!(i => i.classinfo)(k.interfaces);
     auto b = only(k.base);

     // Types
     alias M = typeof(m);
     alias B = typeof(b);

     // Element types
     alias EM = ElementType!M;
     alias EB = ElementType!B;

     // Two of chain's constraints are satisfied:
     static assert(isInputRange!M);
     static assert(isInputRange!B);
     // Now it needs to see a CommonType of range elements

     pragma(msg, EM);    // const(void)[]()
     pragma(msg, EB);    // const(void)[]()

     pragma(msg, CommonType!(EM, EB)); // void

     // For that reason, the following does not work:
     // chain(m, b);
}

Ali
Jul 04 2017
parent reply Jean-Louis Leroy <jl leroy.nyc> writes:
On Wednesday, 5 July 2017 at 00:28:01 UTC, Ali Çehreli wrote:

 On 07/04/2017 04:57 PM, Jean-Louis Leroy wrote:

[...]


 No time to dig deeper but this is because the two ranges that 
 chain() receives do not have a common type. (Rather, that type 
 is 'void'):

 [...]


I suspect that that is the reason, although I checked in several 
ways that I had ClassInfo elements on both sides. Ok, I'll keep 
looking tomorrow with a fresh eye...
Jul 04 2017
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 07/04/2017 05:52 PM, Jean-Louis Leroy wrote:

 On Wednesday, 5 July 2017 at 00:28:01 UTC, Ali Çehreli wrote:

 On 07/04/2017 04:57 PM, Jean-Louis Leroy wrote:

 [...]


 No time to dig deeper but this is because the two ranges that chain()
 receives do not have a common type. (Rather, that type is 'void'):

 [...]


 I suspect that that is the reason, although I checked in several ways
 that I had ClassInfo elements on both sides. Ok, I'll keep looking
 tomorrow with a fresh eye...


This is related to TypeInfo.init, which unfortunately is *not* the .init 
property in this case. :( Luckily, it will be fixed in 2.075. This is 
what object.d has:

class TypeInfo
{
// ...

     /**
      * Return default initializer.  If the type should be initialized 
to all
      * zeros, an array with a null ptr and a length equal to the type 
size will
      * be returned. For static arrays, this returns the default 
initializer for
      * a single element of the array, use `tsize` to get the correct size.
      */
     abstract const(void)[] initializer() nothrow pure const  safe  nogc;

     /// $(RED Removed.) Please use `initializer` instead.
      disable static const(void)[] init(); // since 2.074
     /* Planned for 2.075: Remove init, making way for the init type 
property,
     fixing issue 12233. */
}

The problem is, ElementType relies on .init, which works on most other 
type but not TypeInfo:

template ElementType(R)
{
     static if (is(typeof(R.init.front.init) T))
         alias ElementType = T;
     else
         alias ElementType = void;
}

So, unfortunately, most Phobos range functions cannot be used with 
TypeInfo as they would invariably touch ElementType. Here is a halfway 
workaround that uses each() instead of map(): :/

import std.algorithm;

class C {
}

void main() {
     auto k = C.classinfo;

     TypeInfo_Class[] arr;

     each!(i => arr ~= i.classinfo)(k.interfaces);
     arr ~= k.base;
}

Ali
Jul 04 2017
parent Jean-Louis Leroy <jl leroy.nyc> writes:
On Wednesday, 5 July 2017 at 01:43:46 UTC, Ali Çehreli wrote:

 On 07/04/2017 05:52 PM, Jean-Louis Leroy wrote:

 On Wednesday, 5 July 2017 at 00:28:01 UTC, Ali Çehreli wrote:

 On 07/04/2017 04:57 PM, Jean-Louis Leroy wrote:

 [...]


 No time to dig deeper but this is because the two ranges that 
 chain()
 receives do not have a common type. (Rather, that type is 
 'void'):

 [...]




 This is related to TypeInfo.init, which unfortunately is *not* 
 the .init property in this case. :( Luckily, it will be fixed 
 in 2.075. This is what object.d has:
 [...]
 So, unfortunately, most Phobos range functions cannot be used 
 with TypeInfo as they would invariably touch ElementType. Here 
 is a halfway workaround that uses each() instead of map(): :/


Aaah, so I was not doing anything wrong ;-)

I was trying to factor this code:

       foreach (i; k.interfaces) {
         if (i.classinfo in classMap) {
           v.bases ~= classMap[i.classinfo];
         }
       }
       if (k.base in classMap) {
         v.bases ~= classMap[k.base];
       }

i.e. process the class base along with the interfaces in the same 
loop. I dwelled on it because my goal with this project is to 
learn (and evaluate) D.

Anyway, I am building my own graph of enriched ClassInfo objects; 
once that is done, I won't be impacted with the bug anymore.

Thanks for the diagnostic...

J-L
Jul 05 2017
prev sibling parent reply Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Tuesday, 4 July 2017 at 23:27:25 UTC, Jean-Louis Leroy wrote:

 I want to create a range that consists of the result of a map() 
 followed by a value, e.g.:

   int[] x = [ 1, 2, 3];
   auto y = map!(x => x * x)(x);
   auto z = y ~ 99; // how???

 I have tried several variations: convert 99 to a dynamic array, 
 to a range, convert range to dynamic array (couldn't even 
 figure that one); to no avail.

 Help please...


using
    auto y = x.map!(x => x * x).array;
will work.
Jul 04 2017
parent Jonathan M Davis via Digitalmars-d-learn writes:
On Tuesday, July 04, 2017 23:50:57 Nicholas Wilson via Digitalmars-d-learn 
wrote:

 On Tuesday, 4 July 2017 at 23:27:25 UTC, Jean-Louis Leroy wrote:

 I want to create a range that consists of the result of a map()

 followed by a value, e.g.:
   int[] x = [ 1, 2, 3];
   auto y = map!(x => x * x)(x);
   auto z = y ~ 99; // how???

 I have tried several variations: convert 99 to a dynamic array,
 to a range, convert range to dynamic array (couldn't even
 figure that one); to no avail.

 Help please...


 using
     auto y = x.map!(x => x * x).array;
 will work.


Yeah, that will convert the range to a dynamic array, but if you're looking
to do is append onto a range, then using chain like H.S. Teoh showed is
better. And even if you ultimately want a dynamic array, using chain and
then calling array on the result than allocating the array and then
appending to it as an array means that you're only going to allocate the
array once, whereas if you append to the array, you might end up causing it
to be reallocated (though if you're just appending a single element to it
it'll have the space unless in std.array.array allocates a dynamic array
with exactly the space required for its elements, which I doubt).

- Jonathan M Davis
Jul 04 2017