Re: Generate a pointer to a method of a struct
On Saturday, 15 October 2022 at 01:48:15 UTC, kdevel wrote: Is this consistent? I think all the compilers should error on expressions like `Type.nonStaticMethod` and instead there should be a new __traits dedicated to that, especially because `this` is not a formal parameter.
Re: Generate a pointer to a method of a struct
On Saturday, 15 October 2022 at 01:48:15 UTC, kdevel wrote:
$ dmd -unittest -main -run ini
ini.d(6): Error: non-constant expression `& bar`
ini.d(7): Error: non-constant expression `& bar`
```
Is this consistent?
I can attest to consistency using ldc. Each of the following
prevent function address re-assignment:
immutable string function() f =
const string function() f =
enum f =
In contrast, as would be expected, the following has no such
restriction:
string function() f =
Example:
struct S {
string bar(){return "Hello";}
string foo(){return "Goodbye";}
}
void main() {
string function() f =
writeln(f, " ", f());
f =
writeln(f, " ", f());
}
Re: Generate a pointer to a method of a struct
On Saturday, 15 October 2022 at 00:31:47 UTC, Iain Buclaw wrote:
```
auto funcptr (alias method) ()
{
return
}
:
fun = funcptr!bar;
:
```
Which works but neither dmd nor gdc were able to optimize the
additional function call away.
pragma(inline, true)
auto funcptr (alias method) ()
Thanks. Just found that
```
template funcptr (alias method) {
enum funcptr =
}
```
works on both dmd and gdc. This gives rise to questions:
Is this code expected to compile and pass its unittest?
```
struct S {
void bar () { }
}
enum ei =
immutable i = // line 6
const c = // line 7
unittest {
import std.stdio;
writeln (ei);
writeln (i);
writeln (c);
}
```
gdc passes while dmd says:
```
$ dmd -unittest -main -run ini
ini.d(6): Error: non-constant expression `& bar`
ini.d(7): Error: non-constant expression `& bar`
```
Is this consistent?
Re: Generate a pointer to a method of a struct
On Friday, 14 October 2022 at 18:34:58 UTC, kdevel wrote:
dmd and gdc optimize the lambda invocations away. Nonetheless
the expression looks somewhat too big. To overcome this I tried
to generate the function pointer outside of the struct:
```
auto funcptr (alias method) ()
{
return
}
:
fun = funcptr!bar;
:
```
Which works but neither dmd nor gdc were able to optimize the
additional function call away.
pragma(inline, true)
auto funcptr (alias method) ()
Generate a pointer to a method of a struct
Given a struct `S` with method `foo`: Any of these expressions
```
&.S.foo
```
when they occur inside the struct they represent a delegate and
not a function pointer. Is it okay to "extract" and use the
function pointer from the delegate in this way:
```
struct S {
void function () fp;
void foo ()
{
fp = ().funcptr;
}
void bar ()
{
fp = ().funcptr;
}
auto fun () // invocation helper
{
if (! fp)
fp = ().funcptr;
void delegate () dg;
dg.ptr =
dg.funcptr = fp;
return dg ();
}
}
unittest {
S s;
s.fun;
s.fun;
}
```
In [1] Walter suggested to use a "lambda function" which reads
(adopted to structs):
```
struct S {
:
void function (ref S) fp;
:
void foo () {
:
fun = function (ref S self) { return self.bar (); };
:
}
:
}
```
dmd and gdc optimize the lambda invocations away. Nonetheless the
expression looks somewhat too big. To overcome this I tried to
generate the function pointer outside of the struct:
```
auto funcptr (alias method) ()
{
return
}
:
fun = funcptr!bar;
:
```
Which works but neither dmd nor gdc were able to optimize the
additional function call away. So I replaced the function call
with a value:
```
template funcptr (alias method) {
immutable funcptr = // (*)
}
```
That code compiles under gdc 12.1 but I could not find any dmd
version which compiles the code. All say
```
ptrtomethod.d(15): Error: non-constant expression `& bar`
```
Line 15 is the line I marked with `(*)`. Any comments?
[1] https://www.digitalmars.com/articles/b68.html
Member Function Pointers in D
