DLearner via Digitalmars-d-learn wrote:
> On Monday, 4 December 2023 at 21:55:29 UTC, Mike Shah wrote:
> 
> [...]
>>
>> Is something like this what you had in mind?
>>
>> ```
>> void main() {
>>    import std.stdio;
>>
>>    mixin template A() {
>>       int I1;
>>       int I2;
>>       char X;
>>    }
>>
>>    struct B {
>>       mixin A;
>>       int Var1;
>>       int Var2;
>>    }
>>
>>         B someObject;
>>         writeln(someObject.I1);
>>         writeln(someObject.I2);
>> }
>> ```
> 
> More like
> ```
> B someObject;
>           writeln(someObject.Var1);
>           writeln(someObject.Var2);
> ```
> 
> In the areas where B is used, don't want I1 or I2 to be visible.
> 

If you don't want members of A to be visible in B, why are you
even including struct A as part of B?

Why wouldn't you use a class and make the members private?

I'm certainly not a D expert and I don't know your use case
so maybe I'm missing something.

scot

On Mon, Dec 04, 2023 at 11:46:45PM +0000, DLearner via Digitalmars-d-learn wrote: [...]
> Basically, B corresponds to the whole record (and only a whole record
> can be read).
> But the task only requires Var1 and Var2, the last two fields on the record.
> By putting all the irrelevant fields into A, and defining B as above,
> program remains unpolluted with data it does not need.
[...]

Sounds like what you need is something like this:

	struct Record {
		struct UnimportantStuff {
			...
		}
		UnimportantStuff unimportant;

		struct ImportantStuff {
			...
		}
		ImportantStuff important;
	}

	ImportantStuff readData() {
		Record rec = readData(...); // read entire record
		return rec.important; // discard unimportant stuff
	}

	int main() {
		...
		ImportantStuff data = readData(); // only important stuff returned
		processData(data);
		...
	}


T

-- 
Let X be the set not defined by this sentence...

On Monday, December 4, 2023 11:26:07 AM MST DLearner via Digitalmars-d-learn wrote:
> Suppose we need a construct like:
> ```
> void main() {
>
>     struct A {
>        int I1;
>        int I2;
>        char X;
>     }
>
>     struct B {
>        A Dummy;
>        int Var1;
>        int Var2;
>     }
> }
> ```
> But do not want to give an explicit name (like 'Dummy' above) to
> the A struct held within the B struct.
>
> Just removing 'Dummy' does not work (Error: no identifier for
> declarator `A`).
> Nor does replacing 'Dummy' with {}
>
> Suggestions?

Normally, if you're not going to actually use the member variables, then there's no point in them even being there. However, if you need them there for alignment purposes, then you can just make them private.

- Jonathan M Davis