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digitalmars.D.learn - Using std.stdio.File in a class

reply "Spacen Jasset" <spacenjasset mailrazer.com> writes:
I am trying to use file in a class. It doesn't seem to work. File 
is a struct. Are you not supposed to new structs anymore? The 
examples seem to use auto, but that isn't going to work in this 
situation.

Is File a struct to take advantage of Raii?

import std.stdio;

class X
{
     this()
     {
         f = new File("test2", "wt");
     }

     File f;
}


void main()
{
     X x = new X;
}

C:\temp>dmd file.d && file.exe
file.d(7): Error: constructor std.stdio.File.this 
(shared(_iobuf)* handle, strin
g name, uint refs = 1u, bool isPopened = false) is not callable 
using argument t
ypes (File*)

DMD32 D Compiler v2.065
Apr 08 2014
next sibling parent reply "Adam D. Ruppe" <destructionator gmail.com> writes:
On Tuesday, 8 April 2014 at 14:52:02 UTC, Spacen Jasset wrote:

 Are you not supposed to new structs anymore?


Only if they're pointers. new File returns a File*, not a File.

But you shouldn't new a File because then the file won't be 
automatically closed when it goes out of scope (RAII indeed).

Your code should work if you just take out the new keyword.
Apr 08 2014
parent reply "Spacen Jasset" <spacenjasset mailrazer.com> writes:
On Tuesday, 8 April 2014 at 14:53:56 UTC, Adam D. Ruppe wrote:

 On Tuesday, 8 April 2014 at 14:52:02 UTC, Spacen Jasset wrote:

 Are you not supposed to new structs anymore?


 Only if they're pointers. new File returns a File*, not a File.

 But you shouldn't new a File because then the file won't be 
 automatically closed when it goes out of scope (RAII indeed).

 Your code should work if you just take out the new keyword.


Perhaps the new keyword doesn't do what it used to do? I'll have 
to check all this out.
Apr 08 2014
parent reply "Rene Zwanenburg" <renezwanenburg gmail.com> writes:
On Tuesday, 8 April 2014 at 15:08:17 UTC, Spacen Jasset wrote:

 On Tuesday, 8 April 2014 at 14:53:56 UTC, Adam D. Ruppe wrote:

 On Tuesday, 8 April 2014 at 14:52:02 UTC, Spacen Jasset wrote:

 Are you not supposed to new structs anymore?


 Only if they're pointers. new File returns a File*, not a File.

 But you shouldn't new a File because then the file won't be 
 automatically closed when it goes out of scope (RAII indeed).

 Your code should work if you just take out the new keyword.


 Perhaps the new keyword doesn't do what it used to do? I'll 
 have to check all this out.



structs too. In D new allocates something on the GC heap.
Apr 08 2014
parent reply "Spacen Jasset" <spacenjasset mailrazer.com> writes:
On Tuesday, 8 April 2014 at 15:15:37 UTC, Rene Zwanenburg wrote:

 On Tuesday, 8 April 2014 at 15:08:17 UTC, Spacen Jasset wrote:

 On Tuesday, 8 April 2014 at 14:53:56 UTC, Adam D. Ruppe wrote:

 On Tuesday, 8 April 2014 at 14:52:02 UTC, Spacen Jasset wrote:

 Are you not supposed to new structs anymore?


 Only if they're pointers. new File returns a File*, not a 
 File.

 But you shouldn't new a File because then the file won't be 
 automatically closed when it goes out of scope (RAII indeed).

 Your code should work if you just take out the new keyword.


 Perhaps the new keyword doesn't do what it used to do? I'll 
 have to check all this out.



 structs too. In D new allocates something on the GC heap.


I don't think I am confusing it with C hash. I think it's 
changed. I found this in some old code I wrote years ago:

scope Stream file = new File(filename);
Apr 08 2014
parent "Adam D. Ruppe" <destructionator gmail.com> writes:
On Tuesday, 8 April 2014 at 15:52:23 UTC, Spacen Jasset wrote:

 scope Stream file = new File(filename);


That's a std.stream.File which is a class (implementing the 
Stream interface) which is a different animal from 
std.stdio.File, which is a struct.
Apr 08 2014
prev sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 08 Apr 2014 10:52:01 -0400, Spacen Jasset  
<spacenjasset mailrazer.com> wrote:


 I am trying to use file in a class. It doesn't seem to work. File is a  
 struct. Are you not supposed to new structs anymore? The examples seem  
 to use auto, but that isn't going to work in this situation.

 Is File a struct to take advantage of Raii?

 import std.stdio;

 class X
 {
      this()
      {
          f = new File("test2", "wt");
      }

      File f;
 }


 void main()
 {
      X x = new X;
 }

 C:\temp>dmd file.d && file.exe
 file.d(7): Error: constructor std.stdio.File.this (shared(_iobuf)*  
 handle, strin
 g name, uint refs = 1u, bool isPopened = false) is not callable using  
 argument t
 ypes (File*)

 DMD32 D Compiler v2.065


Just a word of caution, I don't think the RAII semantics of File work  
properly in multithreaded code when the File is destroyed by the GC.

-Steve
Apr 08 2014
next sibling parent "monarch_dodra" <monarchdodra gmail.com> writes:
On Tuesday, 8 April 2014 at 15:18:20 UTC, Steven Schveighoffer 
wrote:

 Just a word of caution, I don't think the RAII semantics of 
 File work properly in multithreaded code when the File is 
 destroyed by the GC.

 -Steve


RAII doesn't work correctly with GC, period.
Apr 08 2014
prev sibling parent reply "Spacen Jasset" <spacenjasset mailrazer.com> writes:
On Tuesday, 8 April 2014 at 15:18:20 UTC, Steven Schveighoffer 
wrote:

 On Tue, 08 Apr 2014 10:52:01 -0400, Spacen Jasset 
 <spacenjasset mailrazer.com> wrote:


 I am trying to use file in a class. It doesn't seem to work. 
 File is a struct. Are you not supposed to new structs anymore? 
 The examples seem to use auto, but that isn't going to work in 
 this situation.

 Is File a struct to take advantage of Raii?

 import std.stdio;

 class X
 {
     this()
     {
         f = new File("test2", "wt");
     }

     File f;
 }


 void main()
 {
     X x = new X;
 }

 C:\temp>dmd file.d && file.exe
 file.d(7): Error: constructor std.stdio.File.this 
 (shared(_iobuf)* handle, strin
 g name, uint refs = 1u, bool isPopened = false) is not 
 callable using argument t
 ypes (File*)

 DMD32 D Compiler v2.065


 Just a word of caution, I don't think the RAII semantics of 
 File work properly in multithreaded code when the File is 
 destroyed by the GC.

 -Steve


What do you mean by don't work? I can see that it won't be RAII 
anymore since there is no stack scope. However, I expect it to 
get closed properly - as and when the containing object is 
collected, or when you use the scope keyword with a class object.

Is this not so?
Apr 08 2014
parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Tue, 08 Apr 2014 11:54:45 -0400, Spacen Jasset  
<spacenjasset mailrazer.com> wrote:


 On Tuesday, 8 April 2014 at 15:18:20 UTC, Steven Schveighoffer wrote:

 Just a word of caution, I don't think the RAII semantics of File work  
 properly in multithreaded code when the File is destroyed by the GC.


 What do you mean by don't work? I can see that it won't be RAII anymore  
 since there is no stack scope. However, I expect it to get closed  
 properly - as and when the containing object is collected, or when you  
 use the scope keyword with a class object.

 Is this not so?


The reference count inc/dec is not thread-safe, so if the GC collects your  
object in a thread that is not the original thread, it may be racing with  
your thread that's simultaneously inc/dec the reference count.

What can you do?

1. Single threaded program.
2. destroy the class deterministically with destroy(x);
3. Ensure the file reference is unique, do not share it with any other  
objects.

-Steve
Apr 08 2014