Below is a flagged enum I have:
enum PermissionEnum {
SU = 1 << 0, // 1
Administrator = 1 << 1, // 2
User = 1 << 2 // 4
}
If the value given is 6, how can I achieve:
An array of strings -> ['Administrator', 'User']
An array of numbers -> [2,4]
If you want to convert values in the enum namespace, consider adding a static function for that purpose.
For extracting set bits from a number efficiently, you can use this trick: n & (~n+1) will give you the lowest set bit.
enum PermissionEnum {
SU = 1 << 0, // 1
Administrator = 1 << 1, // 2
User = 1 << 2 // 4
}
namespace PermissionEnum {
export function toValues(n: PermissionEnum) {
const values: string[] = [];
while (n) {
const bit = n & (~n+1);
values.push(PermissionEnum[bit]);
n ^= bit;
}
return values;
}
}
console.log(PermissionEnum.toValues(PermissionEnum.Administrator));
console.log(PermissionEnum.toValues(PermissionEnum.Administrator + PermissionEnum.SU));
The output is:
[ 'Administrator' ]
[ 'SU', 'Administrator' ]
To convert numbers, simply push the bit without needing a lookup table.
Here is a solution that should do the trick:
let roles: RoleEnum = RoleEnum.Admin | RoleEnum.User;
const roleNumbers: number[] = [];
const roleStrings: string[] = [];
let index = 0;
let currentRole: number;
while (RoleEnum[currentRole = 1 << index++]) {
if (roles & currentRole) {
roleNumbers.push(currentRole);
roleStrings.push(RoleEnum[currentRole]);
}
}
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