Re: this is null
On Sunday, 10 March 2019 at 14:25:56 UTC, spir wrote: There is a typo in this instruction: T* ptr = this.list.getFisrtFreeOrAdd(memViewLen).getPtr!T(); ^^ rs (may this explain your null? the compiler should complain) diniz Good catch! But I have the same typo within the definition of the method. I believe DMD screams about undefined method if it happens.
Re: this is null
On 09/03/2019 21:10, ANtlord via Digitalmars-d-learn wrote: On Saturday, 9 March 2019 at 20:04:53 UTC, Paul Backus wrote: You can end up with a null `this` reference if you dereference a null pointer to a struct and then call a method on the result. For example: I can but my reference is not null before calling. Take a look at the line of code [0]. There is a check before the line. https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/mem.d#L20 [0] There is a typo in this instruction: T* ptr = this.list.getFisrtFreeOrAdd(memViewLen).getPtr!T(); ^^ rs (may this explain your null? the compiler should complain) diniz
Re: this is null
On Saturday, 9 March 2019 at 21:00:51 UTC, Ali Çehreli wrote: I haven't run the code but which pointer is null? Try adding I mean `this` by "this" word. You can see that `this` is null if you run gdb and before that line make `p/x this` [0] this check as well: auto node = this.list.getFisrtFreeOrAdd(memViewLen); assert(node !is null); I get segfault in `getFisrtFreeOrAdd` method. Before the line I have an assertion [1]. It looks like the program misses (I have no idea how) `list` object while calling its method `getFisrtFreeOrAdd`. [0] https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/freelist.d#L56 [1] https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/mem.d#L19
Re: this is null
On 03/09/2019 12:10 PM, ANtlord wrote: On Saturday, 9 March 2019 at 20:04:53 UTC, Paul Backus wrote: You can end up with a null `this` reference if you dereference a null pointer to a struct and then call a method on the result. For example: I can but my reference is not null before calling. Take a look at the line of code [0]. There is a check before the line. https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/mem.d#L20 [0] I haven't run the code but which pointer is null? Try adding this check as well: auto node = this.list.getFisrtFreeOrAdd(memViewLen); assert(node !is null); Ali
Re: this is null
On Saturday, 9 March 2019 at 20:04:53 UTC, Paul Backus wrote:
struct S
{
bool isThisNull() { return &this is null; }
}
void main()
{
import.std.stdio;
S* p = null;
writeln((*p).isThisNull); // true
}
Interactive version: https://run.dlang.io/is/fgT2rS
Anyway, thank you! I didn't know about the feature.
Re: this is null
On Saturday, 9 March 2019 at 20:04:53 UTC, Paul Backus wrote: You can end up with a null `this` reference if you dereference a null pointer to a struct and then call a method on the result. For example: I can but my reference is not null before calling. Take a look at the line of code [0]. There is a check before the line. https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/mem.d#L20 [0]
Re: this is null
On Saturday, 9 March 2019 at 19:18:38 UTC, ANtlord wrote:
Hello everyone! I've encountered the problem which I already
encountered before. Unfortunately, I had no time in the
previous time to report and to talk about it. So I decided to
play making my own "malloc" function in pure D (betterC) at
this time. And I encountered the issue one more time. `this`
can be null. How? Please take a look at my project [0]. It gets
the current heap break and tries to increase via a free list.
So the segfault I meet happens there [1]. Tell me, please. What
do I wrong?
[0] https://github.com/ANtlord/deadmemory
[1]
https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/freelist.d#L56
You can end up with a null `this` reference if you dereference a
null pointer to a struct and then call a method on the result.
For example:
struct S
{
bool isThisNull() { return &this is null; }
}
void main()
{
import.std.stdio;
S* p = null;
writeln((*p).isThisNull); // true
}
Interactive version: https://run.dlang.io/is/fgT2rS
this is null
Hello everyone! I've encountered the problem which I already encountered before. Unfortunately, I had no time in the previous time to report and to talk about it. So I decided to play making my own "malloc" function in pure D (betterC) at this time. And I encountered the issue one more time. `this` can be null. How? Please take a look at my project [0]. It gets the current heap break and tries to increase via a free list. So the segfault I meet happens there [1]. Tell me, please. What do I wrong? [0] https://github.com/ANtlord/deadmemory [1] https://github.com/ANtlord/deadmemory/blob/master/src/deadmemory/freelist.d#L56
Re: opCast fails when this is null.
On 28-10-17 16:22, Nicholas Wilson wrote: On Saturday, 28 October 2017 at 14:19:01 UTC, Nicholas Wilson wrote: As Basile mentioned, this is compiler sticking checks in behind your back. The reason it works on new LDC is because #6982 was cherry picked to LDC (1.3?) before it was merged into dmd (not sure what version, I though it was 2.076, but it might have been one of the betas of 2.077) because I needed it for DCompute to build without -release. The only course is to use recent compilers. Erm, 2.077 is not a thing yet. Does it work with 2.076.1? No, it does work with the 2.077 beta tough. -- Mike Wey
Re: opCast fails when this is null.
On Saturday, 28 October 2017 at 14:19:01 UTC, Nicholas Wilson wrote: As Basile mentioned, this is compiler sticking checks in behind your back. The reason it works on new LDC is because #6982 was cherry picked to LDC (1.3?) before it was merged into dmd (not sure what version, I though it was 2.076, but it might have been one of the betas of 2.077) because I needed it for DCompute to build without -release. The only course is to use recent compilers. Erm, 2.077 is not a thing yet. Does it work with 2.076.1?
Re: opCast fails when this is null.
On Saturday, 28 October 2017 at 13:24:49 UTC, Mike Wey wrote:
The following code runs correctly when compiled with ldc
(1.4.0) but fails with an assert error when compiled with dmd
(2.076 and ldc 1.2.0)
```
class A
{
}
class B
{
T opCast(T)()
{
return this;
}
}
void main()
{
A a = null;
B b = null;
auto c = cast(Object)a;
auto d = cast(Object)b; // Fails with:
core.exception.AssertError@test.d(8): null this
}
```
How would you write an opCast that would handle this case
correctly?
Testing if this is null at the start of the opCast doesn't help
since the assert is thrown before that happens.
Making the opCast static leaves us without access to this,
which would be needed in my use case.
We can't relay on ufcs since the rewrite to opCast doesn't
happen when it's not a member function.
As Basile mentioned, this is compiler sticking checks in behind
your back.
The reason it works on new LDC is because #6982 was cherry picked
to LDC (1.3?) before it was merged into dmd (not sure what
version, I though it was 2.076, but it might have been one of the
betas of 2.077) because I needed it for DCompute to build without
-release.
The only course is to use recent compilers.
Re: opCast fails when this is null.
On Saturday, 28 October 2017 at 13:24:49 UTC, Mike Wey wrote:
The following code runs correctly when compiled with ldc
(1.4.0) but fails with an assert error when compiled with dmd
(2.076 and ldc 1.2.0)
```
class A
{
}
class B
{
T opCast(T)()
{
return this;
}
}
void main()
{
A a = null;
B b = null;
auto c = cast(Object)a;
auto d = cast(Object)b; // Fails with:
core.exception.AssertError@test.d(8): null this
}
```
How would you write an opCast that would handle this case
correctly?
Compiler change is required.
This doesn't happen in -release mode. The assert is automatically
generated by the compiler. It could be disabled, as done here for
ctors and dtors
https://github.com/dlang/dmd/pull/6982
opCast fails when this is null.
The following code runs correctly when compiled with ldc (1.4.0) but
fails with an assert error when compiled with dmd (2.076 and ldc 1.2.0)
```
class A
{
}
class B
{
T opCast(T)()
{
return this;
}
}
void main()
{
A a = null;
B b = null;
auto c = cast(Object)a;
auto d = cast(Object)b; // Fails with:
core.exception.AssertError@test.d(8): null this
}
```
How would you write an opCast that would handle this case correctly?
Testing if this is null at the start of the opCast doesn't help since
the assert is thrown before that happens.
Making the opCast static leaves us without access to this, which would
be needed in my use case.
We can't relay on ufcs since the rewrite to opCast doesn't happen when
it's not a member function.
--
Mike Wey
