Re: Changing the class data underneath some reference
On 11/29/17 10:22 PM, Jonathan M Davis wrote: With classes, you could also assign the entire state of the object similar to what you'd get with structs and opAssign, but you'd have to write a member function to do it. There's no reason that you couldn't do the equivalent of opAssign. It's just that there's no built-in operator for it. So, whatever member function you wrote for it would be non-standard. It's mostly a bad idea. The whole point of disallowing assignment is to prevent the slicing problem. It's also why opAssign isn't overloadable for classes assigning to classes in the same hierarchy. -Steve
Re: Changing the class data underneath some reference
On Wednesday, November 29, 2017 21:12:58 Steven Schveighoffer via
Digitalmars-d-learn wrote:
> On 11/29/17 7:40 PM, David Colson wrote:
> > Hello all!
> >
> > I'm getting settled into D and I came into a problem. A code sample
> > shows it best:
> >
> > class SomeType
> > {
> >
> > string text;
> > this(string input) {text = input;}
> >
> > }
> >
> >
> > void main()
> > {
> >
> > SomeType foo = new SomeType("Hello");
> >
> > SomeType bar = foo;
> >
> > foo = new SomeType("World");
> >
> > writeln(bar.text); // Prints hello
> > // I'd like it to print World
> >
> > }
> >
> > In the C++ world I could do this using pointers and changing the data
> > underneath a given pointer, but I can't use pointers in D, so I'm not
> > sure how I can get this behaviour?
> >
> > I'd be open to other ways of achieving the same affect in D, using more
> > D like methods.
>
> D does not support reassigning class data using assignment operator,
> only the class reference. You can change the fields individually if you
> need to.
>
> e.g.:
>
> foo.text = "World";
>
> structs are value types in D and will behave similar to C++
> classes/structs.
With classes, you could also assign the entire state of the object similar
to what you'd get with structs and opAssign, but you'd have to write a
member function to do it. There's no reason that you couldn't do the
equivalent of opAssign. It's just that there's no built-in operator for it.
So, whatever member function you wrote for it would be non-standard. Heck,
technically, we don't even have a standard way to clone a class object like
C# or Java do. Some folks write a clone function and others write a dup
function; either way, there's nothing built-in or standard for it.
- Jonathan M Davis
Re: Changing the class data underneath some reference
On Thursday, 30 November 2017 at 00:40:51 UTC, David Colson wrote:
Hello all!
I'm getting settled into D and I came into a problem. A code
sample shows it best:
class SomeType
{
string text;
this(string input) {text = input;}
}
void main()
{
SomeType foo = new SomeType("Hello");
SomeType bar = foo;
foo = new SomeType("World");
writeln(bar.text); // Prints hello
// I'd like it to print World
}
In the C++ world I could do this using pointers and changing
the data underneath a given pointer, but I can't use pointers
in D, so I'm not sure how I can get this behaviour?
I'd be open to other ways of achieving the same affect in D,
using more D like methods.
You are dealing with a reference type. Reference types can be
though of as a value type of an address. The new operator can be
though of as giving the variable a new address. This means the
foo and bar variables are not bound to the same value because
their referencing different address. You need a struct. Which
isn't a reference.
Re: Changing the class data underneath some reference
On 11/29/17 7:40 PM, David Colson wrote:
Hello all!
I'm getting settled into D and I came into a problem. A code sample
shows it best:
class SomeType
{
string text;
this(string input) {text = input;}
}
void main()
{
SomeType foo = new SomeType("Hello");
SomeType bar = foo;
foo = new SomeType("World");
writeln(bar.text); // Prints hello
// I'd like it to print World
}
In the C++ world I could do this using pointers and changing the data
underneath a given pointer, but I can't use pointers in D, so I'm not
sure how I can get this behaviour?
I'd be open to other ways of achieving the same affect in D, using more
D like methods.
D does not support reassigning class data using assignment operator,
only the class reference. You can change the fields individually if you
need to.
e.g.:
foo.text = "World";
structs are value types in D and will behave similar to C++ classes/structs.
-Steve
Re: Changing the class data underneath some reference
On Thursday, 30 November 2017 at 00:52:25 UTC, codephantom wrote: ... sorry, don't know how the int * got in there ;-) Anyway..who said you can't use pointers in D? Just change: //SomeType bar = foo; SomeType * bar =
Re: Changing the class data underneath some reference
On Thursday, 30 November 2017 at 00:40:51 UTC, David Colson wrote:
Hello all!
I'm getting settled into D and I came into a problem. A code
sample shows it best:
class SomeType
{
string text;
this(string input) {text = input;}
}
void main()
{
SomeType foo = new SomeType("Hello");
SomeType bar = foo;
foo = new SomeType("World");
writeln(bar.text); // Prints hello
// I'd like it to print World
}
In the C++ world I could do this using pointers and changing
the data underneath a given pointer, but I can't use pointers
in D, so I'm not sure how I can get this behaviour?
I'd be open to other ways of achieving the same affect in D,
using more D like methods.
void main()
{
SomeType foo = new SomeType("Hello");
int * ptr;
SomeType * bar;
bar =
foo = new SomeType("World");
writeln(bar.text); // Prints World
}
Re: Changing the class data underneath some reference
On Thursday, 30 November 2017 at 00:40:51 UTC, David Colson wrote:
Hello all!
I'm getting settled into D and I came into a problem. A code
sample shows it best:
class SomeType
{
string text;
this(string input) {text = input;}
}
void main()
{
SomeType foo = new SomeType("Hello");
SomeType bar = foo;
foo = new SomeType("World");
writeln(bar.text); // Prints hello
// I'd like it to print World
}
In the C++ world I could do this using pointers and changing
the data underneath a given pointer, but I can't use pointers
in D, so I'm not sure how I can get this behaviour?
I'd be open to other ways of achieving the same affect in D,
using more D like methods.
I made an example demonstrating what I'd do in C++:
class SomeType
{
public:
std::string text;
SomeType(std::string input) {text = input;}
};
int main()
{
SomeType foo = SomeType("Hello");
SomeType* bar =
foo = SomeType("World");
std::cout << bar->text << "\n"; // Prints World
}
Changing the class data underneath some reference
Hello all!
I'm getting settled into D and I came into a problem. A code
sample shows it best:
class SomeType
{
string text;
this(string input) {text = input;}
}
void main()
{
SomeType foo = new SomeType("Hello");
SomeType bar = foo;
foo = new SomeType("World");
writeln(bar.text); // Prints hello
// I'd like it to print World
}
In the C++ world I could do this using pointers and changing the
data underneath a given pointer, but I can't use pointers in D,
so I'm not sure how I can get this behaviour?
I'd be open to other ways of achieving the same affect in D,
using more D like methods.
