Sumtypes used as C union types not working about v

[felipensp]

Even this example does not works:

#include "@VMODROOT/foo.h"

struct C.Foo {
	a int
}

struct C.Bar {
	a int
}

type Baz = C.Foo | C.Bar

fn main() {
	mut a := Baz{}
	a = C.Foo{a: 1000}
	dump(a)	
}

[spytheman]

the language should provide a way to use V sumtypes as an alias for C union types

V sumtypes are not a direct match to C union types.

However, V union types are a direct match to C union types:

union MyValue {
    x int
    y f32
    z string
}
v1 := MyValue{ x: 123 }
v2 := MyValue{ y: 3.14 }
v3 := MyValue{ z: 'abc' }
unsafe {
    dump(v1.x)
    dump(v2.y)
    dump(v3.z)
}

Note that accessing the fields of an union value is unsafe, since the language has no means to check what the value actually contains.

In contrast a sumtype value, has both a pointer to the actual value, and a type index field in it, and you can determine at runtime what it is.