digitalmars.D.bugs - [Issue 5931] New: keyword new insists on calling a struct's (non-zero argument) constructor--in other words, it won't allow default initialization; also postblit this(this) constructor dosen't get called from "new <structname>(<struct_instance>)"
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http://d.puremagic.com/issues/show_bug.cgi?id=5931
Summary: keyword new insists on calling a struct's (non-zero
argument) constructor--in other words, it won't allow
default initialization; also postblit this(this)
constructor dosen't get called from "new
<structname>(<struct_instance>)"
Product: D
Version: D2
Platform: x86
OS/Version: Mac OS X
Status: NEW
Severity: normal
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: ultimatemacfanatic gmail.com
--- Comment #0 from Christopher the Magnificent <ultimatemacfanatic gmail.com>
2011-05-05 12:08:38 PDT ---
So I need to do this:
class Tokenizer
{
File file;
this(File f)
{
File f2; // default initialized
// problem 1
this.file = new File; // should pointer to return default initialized
File struct but compiler complains
*this.file = f;
// problem 2
this.file = new File(f); // this doesn't work either, notwithstanding
File has a this(this) post-blitter!
}
}
unfortunately, on the line where I make the call to "new File", it gives me
this error:
Error: constructor std.stdio.File.this (string name, in const(char[])
stdioOpenmode = "rb") is not callable using argument types ()
Shouldn't I be able to allocate a default-initialized struct? Or if not,
shouldn't it be allow to have empty-argument struct constructors?
http://www.digitalmars.com/d/2.0/struct.html says empty parameter-list
constructors are not allowed for structs, but why not? Can someone explain
this language decision to me and make a good argument for why it should not be
changed?
when I try "new File(f)" then I get this error message:
tokenizer.d(199): Error: constructor std.stdio.File.this (string name, in
const(char[]) stdioOpenmode = "rb") is not callable using argument types (File)
tokenizer.d(199): Error: cannot implicitly convert expression (file) of type
File to string
It seems to me that the post-blit constructor should be called automatically
when a struct is "function-called" with an instance of the same struct as the
sole parameter like "new S(s_instance)" Don't you agree? You may think this
is a feature request, but when functionality is a departure from what one would
expect, I would tend to call that a bug instead. :-)
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--- Comment #1 from Christopher the Magnificent <ultimatemacfanatic gmail.com>
2011-05-05 19:55:08 PDT ---
This line above (5th line or so)
File file;
should read
File* file;
in other words, the member <file> is supposed to be a pointer to File.
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kennytm gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |kennytm gmail.com
--- Comment #2 from kennytm gmail.com 2011-05-06 01:46:03 PDT ---
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.
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Christopher the Magnificent <ultimatemacfanatic 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 <ultimatemacfanatic 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 -- DOESN"T 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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http://d.puremagic.com/issues/show_bug.cgi?id=5931 --- Comment #4 from kennytm 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 problemThis problem is the same as issue 4249. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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http://d.puremagic.com/issues/show_bug.cgi?id=5931 --- Comment #5 from kennytm gmail.com 2011-05-06 12:48:43 PDT --- (In reply to comment #4)(In reply to comment #3)[snip]I mean issue 4247 -.- -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------At the line above marked "DOESN'T WORK", the compiler refuses to allocate a new default-initialized File struct. This is a problemThis problem is the same as issue 4249.
May 06 2011