[Issue 5931] keyword new won't allow default initialization of a struct where it has a non-zero argument constructor

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https://issues.dlang.org/show_bug.cgi?id=5931

Johannes Loher  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||johannes.lo...@fg4f.de
 Resolution|--- |WONTFIX

--- Comment #6 from Johannes Loher  ---
The first problem mentioned has been solved since 2.063.

The second problem is still present, error message of 2.080.0:

main.d(16): Error: none of the overloads of this are callable using argument
types (File), candidates are:
/usr/include/dlang/dmd/std/stdio.d(387):   
std.stdio.File.this(shared(_IO_FILE)* handle, string name, uint refs = 1u, bool
isPopened = false)
/usr/include/dlang/dmd/std/stdio.d(425):std.stdio.File.this(string
name, const(char[]) stdioOpenmode = "rb")
/usr/include/dlang/dmd/std/stdio.d(443):std.stdio.File.__ctor(R1,
R2)(R1 name) if (isInputRange!R1 && isSomeChar!(ElementEncodingType!R1))
/usr/include/dlang/dmd/std/stdio.d(451):std.stdio.File.__ctor(R1,
R2)(R1 name, R2 mode) if (isInputRange!R1 &&
isSomeChar!(ElementEncodingType!R1) && isInputRange!R2 &&
isSomeChar!(ElementEncodingType!R2))

The reason is in general, that you can't call postblits as if they were
constructors (`File file; auto f = File(file);` also does not work).

However, it seems that postblits will probably be replaced by some form of copy
constructor, so this might even resolve this issue. I will close this for now.
If you really want this feature, please submit a new issue as an enhancement
request.

--

[Issue 5931] keyword new won't allow default initialization of a struct where it has a non-zero argument constructor

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5931


Christopher the Magnificent ultimatemacfana...@gmail.com changed:

   What|Removed |Added

Summary|keyword new insists on  |keyword new won't allow
   |calling a struct's  |default initialization of a
   |(non-zero argument) |struct where it has a
   |constructor--in other   |non-zero argument
   |words, it won't allow   |constructor
   |default initialization; |
   |also postblit this(this)|
   |constructor dosen't get |
   |called from new|
   |structname(struct_instan |
   |ce)   |


--- Comment #3 from Christopher the Magnificent ultimatemacfana...@gmail.com 
2011-05-06 12:32:02 PDT ---
(In reply to comment #2)
 Post-blit is only called when you override the whole structure, as in:
 
 
 import std.stdio;
 
 struct S {
 this(this) {
 writeln(postblit);
 }
 }
 
 void main() {
 S s;
 S t;
 s = t;// -- call postblit on s.
 }
 
 
 Pointer-assignment will *not* call post-blit as you have not blitted
 (memcpy-ed) anything.


*Shouldn't* post-blit be invokable by calling File(file)?  Wouldn't this be a
desirable behavior?

If not, how do I allocate a default-initialized File struct in the heap using
new  (so that I can follow that by overwriting the whole structure and get
post-blitter to run)?

what I'm taking about is this (this is what I want to do):


import std.stdio;

struct Tokenizer
{
File* file = null;

void 
initFile(File f)
{
this.file = new File;   // I want to allocate a new File struct and set
it to File.init -- DOESNT WORK!
*this.file = f;  // copy bits and then automatically call
post-blit File.this(this) 
}
}


At the line above marked DOESN'T WORK, the compiler refuses to allocate a new
default-initialized File struct.  This is a problem

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[Issue 5931] keyword new won't allow default initialization of a struct where it has a non-zero argument constructor

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--- Comment #4 from kenn...@gmail.com 2011-05-06 12:47:28 PDT ---
(In reply to comment #3)
 *Shouldn't* post-blit be invokable by calling File(file)?  Wouldn't this be 
 a
 desirable behavior?
 

Sorry, got distracted by the 'this.file = new File(...)' part because of your
'File file;' :).

No it should not call post-blit directly, because is possible to *declare* such
a constructor. The problem is, should D define the implicitly-defined copy
constructor which does:

struct S {
  this(ref S s) {
this = s;  // implicitly calls the postblit
  }
  ...
}

?

[snip]
 At the line above marked DOESN'T WORK, the compiler refuses to allocate a 
 new
 default-initialized File struct.  This is a problem

This problem is the same as issue 4249.

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[Issue 5931] keyword new won't allow default initialization of a struct where it has a non-zero argument constructor

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--- Comment #5 from kenn...@gmail.com 2011-05-06 12:48:43 PDT ---
(In reply to comment #4)
 (In reply to comment #3)
[snip]
  At the line above marked DOESN'T WORK, the compiler refuses to allocate a 
  new
  default-initialized File struct.  This is a problem
 
 This problem is the same as issue 4249.

I mean issue 4247 -.-

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