It doesn't have what Rust mistakenly calls enums - what everyone else in the world calls sum types, but it most definitely has enums in the traditional sense. Enum normally refers simply to assigning a number to something. That is what iota does.
Yes, those examples too assign a number to something. Enumeration is not a new concept. In fact, it's an incredibly old concept that emerged in programming langauges as a hack to work around our, a the time, limited understanding of type systems. A modern type system has no reason for enums at all. Of course, Go purposefully tries to be an 'old' language, hence why it copied the antiquated pattern of providing assignment of numbers as a language feature.
Not really. Enums as a programming language construct are a 1970s invention.
Funnily enough, Algol 68 had sum types, although controversially so due to overhead concerns. If only Go had copied the state of programming before 1970, then we wouldn't have to listen to all the nonsense about enums sucking. Of course they suck – they are, and always will be, a hack to work around a limited type system.
Go does not have any kind of enumerations, what is has are constants and a gigantic hack for pseudo enumerations, they even compile with broken values!
package main
import "fmt"
type planet int
const (
unknown planet = iota // invalid
mercury // Mercury 0.378,2439.7,3.3e23,57910000,88,0.0000000001,0,false
venus // Venus 0.907,6051.8,4.87e24,108200000,225,92,0,false
earth // Earth 1,6378.1,5.97e24,149600000,365,1,1,false
mars // Mars 0.377,3389.5,6.42e23,227900000,687,0.01,2,false
jupiter // Jupiter 2.36,69911,1.90e27,778600000,4333,20,4,true
saturn // Saturn 0.916,58232,5.68e26,1433500000,10759,1,7,true
uranus // Uranus 0.889,25362,8.68e25,2872500000,30687,1.3,13,true
neptune // Neptune 1.12,24622,1.02e26,4495100000,60190,1.5,2,true
)
func main() {
landingOn := venus
fmt.Printf("Landing on %d\n", landingOn)
landingOn = 42 // What a hack!
fmt.Printf("Landing on %d\n", landingOn)
}
#include <stdio.h>
enum planet {
unknown,
mercury
/* ... */
};
int main() {
planet landingOn = mercury;
printf("Landing on %d\n", landingOn);
landingOn = planet(42); // What a hack!
printf("Landing on %d\n", landingOn);
}
Value constraints have nothing to do with enums. Enums are exclusively about numbering – and as your code shows, the numbering works just fine. Value constraints are an independent feature. One that Go (and C) lack completely, not just in the case of enum values. You can compile with broken values throughout. Consider:
type EmailAddress string
var email EmailAddress = "Not an email address" // A-OK!
Compare that with a language with a more advanced type system like, say, Typescript:
type EmailAddress = `${string}@${string}`
let email: EmailAddress = 'Not an email address' // Compiler error
You can probably make a good case that Go would benefit from value constraints, among other features, but if you're going to start adding such features, why have enums at all? Again, they're a hack to work around a limited type system. If your type system isn't limited...
Pascal doesn't really have enums as a language feature, so there is no direct analog. It has enums as an implementation detail, but for all intents and purposes the language could be implemented with something other than enums. The same is not true of C or Go, which make enums a first-class citizen of the language.
That is, with the caveat that Pascal does allow the union to be converted to its underlying enum representation. If we provide such conversion to get at the enum, then sure:
Program Lander(output);
type
planet = (unknown, mercury);
var
landingOn: Integer;
begin
landingOn := Ord(mercury);
writeln('Landing on ', landingOn);
landingOn := 42;
writeln('Landing on ', landingOn);
end.
But you're ultimately comparing apples and oranges.
Indeed. Just as I explained, Pascal doesn't really have language support for enums. The pseudo 'sum types' abstraction works to try and hide the fact that enums exist, only presenting the implementation detail enum if you explicitly convert a union element to its enumerated ordinal – which, as it happens, is an integer type.
The program is correct – it complies and runs just fine – but the original ask was faulty. Without any kind of real enum support in Pascal the language, there is no way to perform the same operations as is possible in languages that do have natural enum support. This program is the best you are going to do in the absence of that support. This was all detailed earlier.
Again, you are trying to compare apples and oranges. Rust[1] may try as it might to call sum types enums, but enums and sum types – along with Pascal's pseudo 'sum types' – are different models. I understand where your confusion stems from as there are a lot of similarities, but there is also a difference.
[1] And Swift originally, but its documentation is updated to make clear that, contrary to what the name implies, the language's enum construct is actually sum types and not enums.
