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digitalmars.D - Custom Type Unions

reply Dhruv Singal <dsingal calpoly.edu> writes:
I'm trying to implement an interpreter in D as a class project. 
Having already written the the parser and interpreter in Racket, 
I'm having trouble figuring out if dlang has a way for me to 
create a union object that can be one of many object and have it 
be a first-class object, ie it can be the return type of 
functions. Is this something dlang supports? If not, is there a 
better way of implementing this?
Below is some rudimentary code I wrote to test this:
import std.stdio;
import std.string;
alias string = immutable(char)[];
union Value {real realV; bool booV; string stringV; primV prim;};

struct primV{
     real function(int, int) doer;
}
real add (int a, int b){
     real sum = a+b;
     return cast(real)sum;
}
void main(){
         writeln("Beginning Interp");
         primV adder = primV(&add);
         real x = adder.doer(5,6);
         writeln(x);
         }
May 26
parent Dennis <dkorpel gmail.com> writes:
On Sunday, 26 May 2019 at 17:59:21 UTC, Dhruv Singal wrote:
 I'm having trouble figuring out if dlang has a way for me to 
 create a union object that can be one of many object and have 
 it be a first-class object, ie it can be the return type of 
 functions. Is this something dlang supports?
Structs and unions can be returned in D. You can implement a tagged union [1] yourself with them, or use an existing library solution. The standard library has std.variant [2], but I'd recommend the sumtype package [3] (see the 'Features' section in the package description). [1] https://en.wikipedia.org/wiki/Tagged_union [2] https://dlang.org/phobos/std_variant.html [3] http://code.dlang.org/packages/sumtype
May 26