Re: Accessing part of a struct in an easy way

[vit via Digitalmars-d-learn]

On Monday, 3 July 2017 at 13:53:45 UTC, Paolo Invernizzi wrote:

I've struct like that:

struct Foo {
    int a_1; float a_2; string a_3;
    string b_1; double b_2;
}

I would like to transparently access that like:

foo.a.first
foo.b.second = "baz";

with an helper like:

auto a(...) { ... }
auto b(...) { ... }

that can be used also in functions that are expecting it:

void worksOnA( .... ) { }
void worksOnB( .... ) { }

auto foo = Foo( ... )
foo.a.worksOnA();
foo.b.worksOnB();

But I'm struggling in finding a good way to do it...
Suggestions?

Thanks!
/Paolo

//https://dpaste.dzfl.pl/d59469c264b2

import std.algorithm : map, copy, equal;
import std.range : iota;

struct Foo {
    int[3] a;
    string[2] b;
}

ref T first(R : T[], T)(ref R x,){return x[0];}
ref T second(R : T[], T)(ref R x){return x[1];}

void worksOnA(R : int[N], size_t N)(ref R r) {
        iota(1, N+1)
                .map!(x => cast(int)x*2)
                .copy(r[]);
}
void worksOnB(string[] r) { }


void main(){
        auto foo = Foo();
        
        foo.a.first = 1;
        foo.a.second = 2;
        assert(foo.a.first == 1);
        assert(foo.a.second == 2);

        
        foo.b.second = "test";
        assert(foo.b.first == "");
        assert(foo.b.second == "test");
        
        foo.a.worksOnA();
        assert(foo.a[].equal([2, 4, 6]));

}