Re: Filling an array

[user42 via Digitalmars-d-learn]

On Saturday, 12 March 2016 at 18:33:16 UTC, Alex wrote:

On Saturday, 12 March 2016 at 16:37:25 UTC, user42 wrote:

On Saturday, 12 March 2016 at 14:33:19 UTC, Alex wrote:

/snip


I thought this was supposed to halt with an error rather than 
compile and set all members to 1.
The syntax, to me anyways, doesn't really communicate the 
intention of: set all members to 1.

//arr[] = 1;


Whereas the following does

fill(arr, 1);


Well, this was not the question. As stated here:
https://dlang.org/spec/arrays.html
in the section "array setting", it is possible to set an array 
in such a manner. And my question was, why a specific array 
behaves not as expected.
So, either there is a problem with filling an array, or, there 
is a problem with implicit conversion of a Nullable!T to its 
underlying type.


Learned something new. I guess I missed that detail when I read 
that page.

Re: Filling an array

[user42 via Digitalmars-d-learn]

On Saturday, 12 March 2016 at 14:33:19 UTC, Alex wrote:

/snip


I thought this was supposed to halt with an error rather than 
compile and set all members to 1.
The syntax, to me anyways, doesn't really communicate the 
intention of: set all members to 1.

//arr[] = 1;


Whereas the following does

fill(arr, 1);

Re: Why is it not possible to write to a file from a const member function ?

[user42 via Digitalmars-d-learn]

On Saturday, 12 March 2016 at 15:32:39 UTC, Mike Parker wrote:

On Saturday, 12 March 2016 at 14:02:31 UTC, user42 wrote:


Why is this thing not compiling ?
Or, in other words, how is is possible to log something to a 
file from a const member function ?




Const member functions functions are not allowed to mutate any 
member state at all. This includes the state of any object 
instances that are members. Since the write method of the File 
type is not declared as const, then you can not call it on a 
member of type File from inside a const member function. 
Logging, by its very definition, mutates state.


Move the File instance outside of the class and it works.

import std.stdio;
private File f;
static this() { f = stdout; }

class X
{
  void p(string s) const
  {
 f.writeln!(string)(s);
  }
}

class Y
{
  private string s = "Y";

  override string toString() const
  {
 return s;
  }
}

void main()
{
  auto x = new X;
  auto y = new Y;

  import std.conv: to;
  x.p(to!string(y));
}


Thanks for your reply.
Unfortunately it only solves the problem for this particular 
snippet.


The most interesting part of your reply is this line:
Since the write method of the File type is not declared as 
const,


At a quick glance I suppose it's because of the locking in 
LockingTextWriter.


I think I will probably pass this stuff to a C implementation, or 
override toString non-const, since adding const to it started 
this const avalanche in the first place.


Anyways, thanks for your input and have a nice weekend.

Why is it not possible to write to a file from a const member function ?

[user42 via Digitalmars-d-learn]

Hi

I have the following snippet to illustrate my problem/question:

class X
{
  import std.stdio: write, File, stdout;

  private File* f = 

  void p(string s) const
  {
 f.write(s);
  }
}

class Y
{
  private string s = "Y";

  override string toString() const
  {
 return s;
  }
}

void main()
{
  auto x = new X;
  auto y = new Y;

  import std.conv: to;
  x.p(to!string(y));
}

Why is this thing not compiling ?
Or, in other words, how is is possible to log something to a file 
from a const member function ?


Thanks in advance