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Flow is improperly narrowing getter values #56899
Description
🔎 Search Terms
getter narrowing
function return narrowing
an issue where setter (not getter) is behaving like a plain property: #56894
🕗 Version & Regression Information
same 4.3.5 ~ 5.2.3
prior to 4.3.5 TypeScript rejected the syntax.
⏯ Playground Link
💻 Code
function f10(x: { get r():1|2; readonly v: 1| 2; f:()=>1|2 }): void{
// ^ (parameter) x: { readonly r: 1 | 2; readonly v: 1 | 2; f: () => 1 | 2; }
if (x.v===1){
x.v;
// ^ (property) v: 1
}
if (x.r===1){
const c = x.r;
// ^ (property) r: 1
// ^ const c: 1
}
if (x.f()===1){
const c = x.f();
// ^ (property) f: () => 1 | 2
// ^ const c: 1 | 2
}
}🙁 Actual behavior
if (x.r===1){
const c = x.r;
// ^ (property) r: 1
// ^ const c: 1
}🙂 Expected behavior
if (x.r===1){
const c = x.r;
// ^ (property) get r: () => 1 | 2
// ^ const c: 1 | 2
}Additional information about the issue
- A getter is a function, not a plain type, and should behave like one, even though it doesn't have wings.
- The getter is converted to a readonly plain property (probably at point of declaration) as can be seen by tool tipping to
xwhich shows(parameter) x: { readonly r: 1 | 2; readonly v: 1 | 2; f: () => 1 | 2; }. Related to setter inferred from union has incorrect variance #56894.
Activity
fatcerberus commentedon Dec 29, 2023
Duplicate of #56149. That TypeScript is “lossy” and encodes the getter as a regular property in the type is more or less by design.
fatcerberus commentedon Dec 29, 2023
Maybe some day we could have a
volatilekeyword, like C…craigphicks commentedon Dec 30, 2023
Oh what a shame. Now if #56894 is deemed a fixable bug, then setters will be acting like (and hopefully displayed as) functions, while getters will be acting like (and continue to be displayed as?) readonly plain properties. Maybe it would be best to do them as a pair, with a flag of course for back compatibility. Just thinking out loud. Pay no notice.
typescript-bot commentedon Jan 5, 2024
This issue has been marked as "Working as Intended" and has seen no recent activity. It has been automatically closed for house-keeping purposes.