Re: minElement on array of const objects

2017-11-14 Thread Aurelien Fredouelle via Digitalmars-d-learn 

On Monday, 13 November 2017 at 14:28:27 UTC, vit wrote:

On Monday, 13 November 2017 at 12:15:26 UTC, Nathan S. wrote:

[...]


Is Unqual necessary here?:
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1284
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1340

And here
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1301
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1355
is necessary something like RebindableOrUnqual instead of 
Unqual:


template RebindableOrUnqual(T){
	static if (is(T == class) || is(T == interface) || 
isDynamicArray!T || isAssociativeArray!T)alias 
RebindableOrUnqual = Rebindable!T;

else alias RebindableOrUnqual = Unqual!T;
}


Thanks, I filed https://issues.dlang.org/show_bug.cgi?id=17982 to 
track the issue.

Re: minElement on array of const objects

2017-11-13 Thread vit via Digitalmars-d-learn 

On Monday, 13 November 2017 at 12:15:26 UTC, Nathan S. wrote:

Unqual!Element seed = r.front;



alias MapType = Unqual!(typeof(mapFun(CommonElement.init)));


This looks like a job for std.typecons.Rebindable!(const A) 
instead of Unqual!(const A) which is used currently. I am 
surprised that this is the first time anyone has run into this.


Is Unqual necessary here?:
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1284
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1340

And here
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1301
https://github.com/dlang/phobos/blob/master/std/algorithm/searching.d#L1355
is necessary something like RebindableOrUnqual instead of Unqual:

template RebindableOrUnqual(T){
	static if (is(T == class) || is(T == interface) || 
isDynamicArray!T || isAssociativeArray!T)alias RebindableOrUnqual 
= Rebindable!T;

else alias RebindableOrUnqual = Unqual!T;
}

Re: minElement on array of const objects

2017-11-13 Thread Nathan S. via Digitalmars-d-learn 

Unqual!Element seed = r.front;



alias MapType = Unqual!(typeof(mapFun(CommonElement.init)));


This looks like a job for std.typecons.Rebindable!(const A) 
instead of Unqual!(const A) which is used currently. I am 
surprised that this is the first time anyone has run into this.

Re: minElement on array of const objects

2017-11-13 Thread Temtaime via Digitalmars-d-learn 
On Monday, 13 November 2017 at 10:20:51 UTC, Aurelien Fredouelle 
wrote:

Hi all,

It seems that it is not possible to use minElement on an array 
of const objects:


class A
{
  int val;
}

const(A) doStuff(const(A)[] v)
{
  import std.algorithm.searching : minElement;
  return v.minElement!"a.val";
}

This gets the following compiler error:

std/algorithm/searching.d(1256,28): Error: cannot implicitly 
convert expression (front(r)) of type const(A) to app.A
std/algorithm/searching.d(1286,35): Error: cannot implicitly 
convert expression (r[i]) of type const(A) to app.A
std/algorithm/searching.d(1258,36): Error: template instance 
std.algorithm.searching.extremum!("a.val", "a < b", const(A)[], 
A) error instantiating
std/algorithm/searching.d(3345,24):instantiated from 
here: extremum!("a.val", "a < b", const(A)[])
source/app.d(11,11):instantiated from here: 
minElement!("a.val", const(A)[])


Is there a reason why this is not allowed? Shouldn't minElement 
be able to return a const(A) in this situation?


Thanks,
Aurelien


It should not until it uses recursion to find min element.

const(Class) res = ...;
...
return res;

Algorithm tries to assign to res variable and fails because in D 
const(Class) means both const object and const reference to it. 
So we cannot assign another reference to const(Class) variable.

minElement on array of const objects

2017-11-13 Thread Aurelien Fredouelle via Digitalmars-d-learn 

Hi all,

It seems that it is not possible to use minElement on an array of 
const objects:


class A
{
  int val;
}

const(A) doStuff(const(A)[] v)
{
  import std.algorithm.searching : minElement;
  return v.minElement!"a.val";
}

This gets the following compiler error:

std/algorithm/searching.d(1256,28): Error: cannot implicitly 
convert expression (front(r)) of type const(A) to app.A
std/algorithm/searching.d(1286,35): Error: cannot implicitly 
convert expression (r[i]) of type const(A) to app.A
std/algorithm/searching.d(1258,36): Error: template instance 
std.algorithm.searching.extremum!("a.val", "a < b", const(A)[], 
A) error instantiating
std/algorithm/searching.d(3345,24):instantiated from 
here: extremum!("a.val", "a < b", const(A)[])
source/app.d(11,11):instantiated from here: 
minElement!("a.val", const(A)[])


Is there a reason why this is not allowed? Shouldn't minElement 
be able to return a const(A) in this situation?


Thanks,
Aurelien