What am I doing wrong here?
JG
someone at somewhere.com
Sun May 8 09:36:38 UTC 2022
On Saturday, 7 May 2022 at 02:29:59 UTC, Salih Dincer wrote:
> On Friday, 6 May 2022 at 18:04:13 UTC, JG wrote:
>> ```d
>> //...
>> struct Adder {
>> int a;
>> int opCall(int b) { return a+b; }
>> }
>> auto adder(int a) {
>> auto ret = Adder.init;
>> ret.a=a;
>> return ret;
>> }
>>
>> void main() {
>> auto g = adder(5);
>> g(5).writeln; // 10
>> auto d = toDelegate!(int, int)(g);
>> d(5).writeln; // 10
>> // ...
>> }
>> ```
>
> The value returned by the delegate structure in the above line
> is 10. Its parameter is 5, but if you do it to 21, you will get
> 42. So it doesn't have the ability to delegate Adder.
>
> In summary, the sum function isn't executing. Instead, its
> value gets double.
>
> SDB at 79
What do you mean?
```d
import std;
struct Delegate(A,B) {
B function(void* ptr, A a) f;
void* data;
B opCall(A a) {
return f(data,a);
}
}
auto toDelegate(A, B,S)(ref S s) {
static B f(void* ptr, A a) {
return (*(cast(S*) ptr))(a);
}
Delegate!(A,B) ret;
ret.f=&f;
ret.data= cast(void*) &s;
return ret;
}
struct Adder {
int a;
int opCall(int b) { return a+b; }
}
auto adder(int a) {
auto ret = Adder.init;
ret.a=a;
return ret;
}
void main() {
auto g = adder(5);
g(5).writeln;
auto d = toDelegate!(int, int)(g);
d(41).writeln;
auto a =7;
auto h = (int b)=>a+b;
auto d1 = toDelegate!(int,int)(h);
void* ptr = cast(void*) &h;
(*cast(int delegate(int)*) ptr)(10).writeln;
d1(21).writeln;
h(32).writeln;
}
```
Output:
10
46
17
28
39
Which is what is expected.
More information about the Digitalmars-d-learn
mailing list