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Inferred return type for function that return type assertion should be is [type] #14891
Description
TypeScript Version: 2.2.1
Code
function isString(x: any) {
return typeof x === 'string';
}Expected behavior:
Inferred type of foo is function isString(x: any): boolean
Actual behavior:
Inferred type should be function isString(x: any): x is string
Activity
mhegazy commentedon Mar 28, 2017
Related to #5101 (and #10734 tangentially)
I believe we discussed this before in the past, and concluded it was too complex to implement in the general case. doing it right needs to combine control-flow analysis with some sort of data flow analysis.