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digitalmars.D - Access to intersection fields of an algebraic data type

reply sighoya <sighoya gmail.com> writes:
Is there a solution for the following problem:

import std.variant : Algebraic;

struct A
{
     int a=2;
}

struct B
{
     int a=2;
};

void main()
{
     Algebraic!(A,B) c=A();
     writeln(c.a);
     return;
}

Error: no property a for type VariantN!(4LU, A, B)
Jan 19 2019
next sibling parent reply Meta <jared771 gmail.com> writes:
On Saturday, 19 January 2019 at 17:40:53 UTC, sighoya wrote:

 Is there a solution for the following problem:

 import std.variant : Algebraic;

 struct A
 {
     int a=2;
 }

 struct B
 {
     int a=2;
 };

 void main()
 {
     Algebraic!(A,B) c=A();
     writeln(c.a);
     return;
 }

 Error: no property a for type VariantN!(4LU, A, B)


You want the untyped version of std.variant.visit:

writeln(c.visit!(aOrB => aOrB.a));
Jan 19 2019
parent sighoya <sighoya gmail.com> writes:
On Saturday, 19 January 2019 at 17:51:58 UTC, Meta wrote:

 On Saturday, 19 January 2019 at 17:40:53 UTC, sighoya wrote:

 Is there a solution for the following problem:

 import std.variant : Algebraic;

 struct A
 {
     int a=2;
 }

 struct B
 {
     int a=2;
 };

 void main()
 {
     Algebraic!(A,B) c=A();
     writeln(c.a);
     return;
 }

 Error: no property a for type VariantN!(4LU, A, B)


 You want the untyped version of std.variant.visit:

 writeln(c.visit!(aOrB => aOrB.a));


Thanks  Meta,

With the help of dlang's UFCS, we can rewrite it more 
idiomatically as:

import std.variant : Algebraic;

struct A
{
     int a=2;
}

struct B
{
     int a=2;
};

int a(Algebraic!(A,B) c)
{
     return cast(int)(visit!((c)=>c.a)(c));
}

void main()
{
     Algebraic!(A,B) c=A();
     writeln(c.a);
     return;
}
Jan 19 2019
prev sibling parent Nicholas Wilson <iamthewilsonator hotmail.com> writes:
On Saturday, 19 January 2019 at 17:40:53 UTC, sighoya wrote:

 Is there a solution for the following problem:

 import std.variant : Algebraic;

 struct A
 {
     int a=2;
 }

 struct B
 {
     int a=2;
 };

 void main()
 {
     Algebraic!(A,B) c=A();
     writeln(c.a);
     return;
 }

 Error: no property a for type VariantN!(4LU, A, B)


Try using http://code.dlang.org/packages/taggedalgebraic I find 
it much better.
Jan 19 2019