So far, private fields are introduced as follows:
class MyClass {
#privateField = 123;
}
I’d like to propose a small extension: scoped private fields.
The following style is becoming popular in the JavaScript world. It benefits from scoped privacy:
private #data;
function createStringBuilder() {
return {
#data: '',
};
}
function add(sb, str) {
sb.#data += str;
}
function toString(sb) {
return sb.#data;
}
New in this code:
- The keyword
private
in the first line. - The ability to use private fields in object literals.
As a slight downside, you now always need to use the keyword private
:
class StringBuilder {
private #data = ''; // keyword is required
add(str) {
this.#data += str;
}
toString() {
return this.#data;
}
}
On the upside, this gives you the freedom to widen the scope of privacy:
private #data;
class StringBuilder {
#data = ''; // no keyword!
add(str) {
this.#data += str;
}
}
function toString(stringBuilder) {
return stringBuilder.#data;
}
Alternative syntax has been proposed:
- Keyword
private
not needed for “normal” private fields. - Two keywords if you want to widen the scope of privacy:
private
andouter
.
Example:
private #data;
class StringBuilder {
outer #data = ''; // keyword is now required
add(str) {
this.#data += str;
}
}
function toString(stringBuilder) {
return stringBuilder.#data;
}
FP example:
private #data;
function createStringBuilder() {
return {
outer #data: '', // keyword is now required
};
}
function add(sb, str) {
sb.#data += str;
}
function toString(sb) {
return sb.#data;
}
I'd like to second @simon-robertson's comment.
private
is already a reserved word in the language, and is used for declaring private props/methods in C#, Java, Ruby and more. So why choose to use a symbol (which does not explain itself and whose purpose cannot be inferred by reading) instead of the same reserved keyword used for the same purpose in other languages?Is it too late to just throw the inscrutable '#' character idea in the bin (or deprecate its use) and just use the private keyword by itself?