Re: Modify const reference data
Apparently the OP intended to set it in foo(). If the data is
actually mutable and there really is no way other than going
against the type system, foo() must be called at least once and
can be implemented like this:
public void foo()
{
abc = [1,2,3,4];
cast(ubyte*)data = abc.ptr;
}
// ...
B b = new B();
b.foo();
b.print(); // now OK
Ali
Wow, i didn't know i could cast out constness from an lvalue.
This is what i needed. I'll try it in my code as soon as i can.
Thanks.
Re: Modify const reference data
Wow, i didn't know i could cast out constness from an lvalue. This is what i needed. I'll try it in my code as soon as i can. Thanks. Yep, it compiles and works! By the way, i forgot to call b.foo() in my example. Thanks for your help guys.
Modify const reference data
[DMD 2.064.2]
Hello,
I've been strugling with a solution before bothering you guys
here (again). I have my own complex code but i made a VERY simple
test case to reproduce my problem, here's the code:
private import std.stdio;
class A
{
private const ubyte* data;
private ubyte[] abc;
this()
{
abc = [1,2,3,4];
data = cast(const ubyte*)abc.ptr;
}
public void print()
{
for(size_t i = 0; i 4; i++)
{
writefln(%d, data[i]);
}
}
}
class B
{
private const ubyte* data;
private ubyte[] abc;
this()
{
data = cast(const ubyte*)abc.ptr;
}
public void foo()
{
abc = [1,2,3,4];
}
public void print()
{
for(size_t i = 0; i 4; i++)
{
writefln(%d, data[i]);
}
}
}
void main()
{
A a = new A();
a.print(); // OK.
B b = new B();
b.print(); // Crash.
}
The thing is that i can not use the data that const variable
data in class B is referencing because in my original code i
get Invalid Memory Operation, in the test case i get access
violation but it doesn't matter the name of the exception, the
only thing that matters is that the exception raises for the same
reason. I understand that i should not modify the const data
outside a constructor but by stricts reason i can't avoid that.
Do you guys have any other aproach to get away with this? (modify
a const reference data and then manipulate that data). THANK YOU
very much in advance. D2 learner by the way.
Re: Modify const reference data
Duhhh! i got the pink avatar by default. That sucks. Pink is just not my color.
Re: Modify const reference data
Easy problem in class B: data is null!
On Monday, 9 December 2013 at 02:53:01 UTC, Heinz wrote:
class B
{
private const ubyte* data;
private ubyte[] abc;
this()
{
data = cast(const ubyte*)abc.ptr;
}
Since abc isn't initialized in this constructor, abc.ptr is null.
So data is null too.
public void print()
{
for(size_t i = 0; i 4; i++)
{
writefln(%d, data[i]);
}
}
}
And since data is null, data[i] will be a memory
err/segfault/access violation/whatever it is called.
Re: Modify const reference data
On 12/08/2013 07:24 PM, Adam D. Ruppe wrote:
Easy problem in class B: data is null!
On Monday, 9 December 2013 at 02:53:01 UTC, Heinz wrote:
class B
{
private const ubyte* data;
private ubyte[] abc;
this()
{
data = cast(const ubyte*)abc.ptr;
}
Since abc isn't initialized in this constructor, abc.ptr is null. So
data is null too.
public void print()
{
for(size_t i = 0; i 4; i++)
{
writefln(%d, data[i]);
}
}
}
And since data is null, data[i] will be a memory err/segfault/access
violation/whatever it is called.
Apparently the OP intended to set it in foo(). If the data is actually
mutable and there really is no way other than going against the type
system, foo() must be called at least once and can be implemented like this:
public void foo()
{
abc = [1,2,3,4];
cast(ubyte*)data = abc.ptr;
}
// ...
B b = new B();
b.foo();
b.print(); // now OK
Ali
