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Generic conditional type T extends never ? 'yes' : 'no' resolves to never when T is never. · Issue #31751 · microsoft/TypeScript · GitHub
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Working as IntendedThe behavior described is the intended behavior; this is not a bugThe behavior described is the intended behavior; this is not a bug
Description
TypeScript Version: 3.6.0-dev.20190603
Search Terms:
never, extends, generic, conditional type
Code
type MakesSense = never extends never ? 'yes' : 'no' // Resolves to 'yes'
type ExtendsNever<T> = T extends never ? 'yes' : 'no'
type MakesSenseToo = ExtendsNever<{}> // Resolves to 'no'
type Huh = ExtendsNever<never> // Expect to resolve to 'yes', actually resolves to never
Expected behavior:
Huh should resolve to 'yes', as MakesSense does.
Actual behavior:
Huh resolves to never.
For another variant, you can change ExtendsNever to
type ExtendsNever<T extends never> = T extends never ? 'yes' : 'no'
and ExtendsNever still resolves to never.
Playground Link:
Here
Related Issues:
None
someBrown, huan, yinsang, ahamed, boy-bobby and 5 more
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Working as IntendedThe behavior described is the intended behavior; this is not a bugThe behavior described is the intended behavior; this is not a bug
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