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How can I get the scalar type of a pointer to pointer (and in even deeper levels)
Mar 11, 2023
rempas
Mar 11, 2023
ag0aep6g
Mar 11, 2023
rempas
Mar 11, 2023
ag0aep6g
Mar 11, 2023
rempas
March 11, 2023
Gravatar of rempasPosted by rempasReply
rempas
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Let's see the following code:

void test_fn(T)(T val) {
  pragma(msg, "The type of the pointer is: " ~ typeof(*val).stringof);
}

extern (C) void main() {
  int* int_ptr = cast(int*)0x1037;
  char* char_ptr = cast(char*)0x1037;

  test_fn(int_ptr);
  test_fn(char_ptr);
}

This function takes a templates argument that can be any (pointer) type and shows the scalar type of the pointer (at compile time). I'm using the "typeof" operator and I'm referencing the pointer so I can get the scalar type. This will work great for single pointer values but what about pointers to pointers like: int****? Is there a way that I would be able to always get the scalar type of a pointer regardless of how many levels it is? As always, I'm searching for a solution that will work in BetterC.

March 11, 2023
Gravatar of ag0aep6gPosted by ag0aep6g
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On 11.03.23 13:49, rempas wrote:
> but what about pointers to pointers like: `int****`? Is there a way that I would be able to always get the scalar type of a pointer regardless of how many levels it is? As always, I'm searching for a solution that will work in `BetterC`.

alias Foo(T : U*, U) = Foo!U;
alias Foo(T) = T;
static assert(is(Foo!(int*) == int));
static assert(is(Foo!(int**) == int));
static assert(is(Foo!(int***) == int));
static assert(is(Foo!(int****) == int));
March 11, 2023
Gravatar of rempasPosted by rempas
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On Saturday, 11 March 2023 at 12:59:59 UTC, ag0aep6g wrote:
>
> alias Foo(T : U*, U) = Foo!U;
> alias Foo(T) = T;
> static assert(is(Foo!(int*) == int));
> static assert(is(Foo!(int**) == int));
> static assert(is(Foo!(int***) == int));
> static assert(is(Foo!(int****) == int));

Wait, but "Foo" is defined twice and it doesn't let me compile...
March 11, 2023
Gravatar of ag0aep6gPosted by ag0aep6g
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On 11.03.23 14:22, rempas wrote:
> On Saturday, 11 March 2023 at 12:59:59 UTC, ag0aep6g wrote:
>>
>> alias Foo(T : U*, U) = Foo!U;
>> alias Foo(T) = T;
>> static assert(is(Foo!(int*) == int));
>> static assert(is(Foo!(int**) == int));
>> static assert(is(Foo!(int***) == int));
>> static assert(is(Foo!(int****) == int));
> 
> Wait, but "Foo" is defined twice and it doesn't let me compile...

You're doing something wrong then.

Don't put the Foo declarations in a function or unittest.
March 11, 2023
Gravatar of rempasPosted by rempas
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On Saturday, 11 March 2023 at 13:37:26 UTC, ag0aep6g wrote:
> On 11.03.23 14:22, rempas wrote:
>> On Saturday, 11 March 2023 at 12:59:59 UTC, ag0aep6g wrote:
>>>
>>> alias Foo(T : U*, U) = Foo!U;
>>> alias Foo(T) = T;
>>> static assert(is(Foo!(int*) == int));
>>> static assert(is(Foo!(int**) == int));
>>> static assert(is(Foo!(int***) == int));
>>> static assert(is(Foo!(int****) == int));
>> 
>> Wait, but "Foo" is defined twice and it doesn't let me compile...
>
> You're doing something wrong then.
>
> Don't put the Foo declarations in a function or unittest.

Oh, so it tries to re-define them if I put them inside a function! Thank you brother, works great! Have a great day!