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Type inference behave different with or without destructure #28599
Description
TypeScript Version: 3.2.0-dev.201xxxxx
Search Terms: type inference behave different
Code
type Shape = {
kind: 'circle',
data: {
radius: number
}
} | {
kind: 'square',
data: {
size: number
}
};
function getAreaOkay(shape: Shape) {
switch (shape.kind) {
case 'circle':
// okay
return shape.data.radius;
}
}
function getAreaFail({ kind, data }: Shape) {
switch (kind) {
case 'circle':
// fail
return data.radius;
}
}Expected behavior: the above two should be identical.
Actual behavior: they are not.
Activity
AlCalzone commentedon Nov 19, 2018
AFAIK, typescript doesn't narrow the type from one variable (
kind) to a seperate one (data).ahejlsberg commentedon Nov 19, 2018
This is a duplicate of #23613 and several others like it. The core design limitation is that the control flow analyzer doesn't track mutually dependent variables. We're tracking the issue in #12184.
typescript-bot commentedon Dec 12, 2018
This issue has been marked as a duplicate and has seen no activity in the last day. It has been closed automatic house-keeping purposes.