And putting my money where my mouth is... This example could probably be
improved but it covers the basic idea. I looked around for something
already made, but didn't see a simple version which could handle both
implicit value assignment (auto-incrementing values) and explicit
values, never mind a mix of the two. The assignment syntax is not as
clean as I'd like (with the strings/objects), but it's flexible, so
whatever.
For use in QML, put this in an external file:
lib.js:
-----------------
function Enum()
{
this.exists = function(value) {
return (typeof this[value] !== "undefined");
};
let lastValue = 0,
i;
for (i in arguments) {
let arg = arguments[i],
name, value;
if (typeof arg === "object") {
name = Object.keys(arg)[0];
value = Object.values(arg)[0];
}
else if (typeof arg === "string") {
name = arg;
value = lastValue;
}
else {
continue;
}
if (this.exists(name))
throw "Duplicate enum name: " + name;
this[this[name] = value] = name;
lastValue = value + 1;
}
Object.freeze(this); // don't allow modification
}
-------------------
Test.qml:
------------
import QtQuick 2.9
import "lib.js" as Lib
Item {
// ... other properties, etc
readonly property var positions: new Lib.Enum(
'Unspecified', // automatic value, = 0
{BackFace : 5}, // explicit value
'FrontFace' // auto next value, = 6
);
function test() {
console.log(positions.BackFace, positions[positions.BackFace]);
// qml: 5 BackFace
console.log(positions.FrontFace, positions[positions.FrontFace],
positions.exists(positions.FrontFace));
// qml: 6 FrontFace true
// can't change the value, though strangely(?) no error/warning
// even with readonly property
positions["BackFace"] = 25;
console.log(positions.BackFace); // qml: 5
var face = positions.FrontFace;
switch(face) {
case positions.BackFace:
console.log("The back");
break;
case positions.FrontFace:
console.log("The front");
break;
case positions.Unspecified:
console.log("Not specified");
break;
}
// qml: The front
}
Component.onCompleted: test();
}
-------------
JavaScript demo:
https://plnkr.co/edit/p9BM4o2SPtvGB3ZC?open=lib%2Fscript.js&preview
(there's a console view which can be opened on the lower right)
Cheers,
-Max
On 3/20/2020 4:56 AM, Max Paperno wrote:
On 3/20/2020 4:44 AM, Max Paperno wrote:
Obviously one could come up with a little helper function/object which
makes this prettier. And you could make it auto-assign incremental
values if one isn't provided in the "constructor" (like a C enum does)
Err, sorry, I meant a helper object which also provides reverse mapping
from symbol to name.
Something like
var Enum;
(function (Enum) {
Enum[Enum["A"] = 0] = "A";
})(Enum || (Enum = {}));
var a = Enum.A;
var nameOfA = Enum[a]; // "A"
See:
https://www.typescriptlang.org/docs/handbook/enums.html#reverse-mappings
Also their enum type implementation in general seems nice.
-Max
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