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Recursive conditional types #40002

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Merged
ahejlsberg merged 12 commits into from
Aug 16, 2020
Merged

Recursive conditional types #40002

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419e8d6
Support recursive conditional types
ahejlsberg Aug 8, 2020
beab30a
Accept new API baselines
ahejlsberg Aug 8, 2020
c24cacc
Accept new baselines
ahejlsberg Aug 8, 2020
5a45585
Simplify recursive type tracking in type inference
ahejlsberg Aug 10, 2020
4f8dc24
Accept new baselines
ahejlsberg Aug 10, 2020
dd64bf8
Add tests
ahejlsberg Aug 11, 2020
7c4d923
Accept new baselines
ahejlsberg Aug 11, 2020
6c11cf4
Revise recursion tracking in type inference
ahejlsberg Aug 13, 2020
5b45f42
Revise tests
ahejlsberg Aug 13, 2020
fed0e8c
Accept new baselines
ahejlsberg Aug 13, 2020
199d568
Add more tests
ahejlsberg Aug 16, 2020
324b3fb
Accept new baselines
ahejlsberg Aug 16, 2020
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Add more tests
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@ahejlsberg
ahejlsberg committed Aug 16, 2020
commit 199d568785a48a37031c68bf252d1027cb4e5abb
28 changes: 28 additions & 0 deletions tests/cases/compiler/recursiveConditionalTypes.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
// @strict: true
// @declaration: true
// @target: esnext

// Awaiting promises

Expand Down Expand Up @@ -57,6 +58,33 @@ declare function f23<T>(t: TupleOf<T, 3>): T;

f23(['a', 'b', 'c']); // string

// Inference to recursive type

interface Box<T> { value: T };
type RecBox<T> = T | Box<RecBox<T>>;
type InfBox<T> = Box<InfBox<T>>;

declare function unbox<T>(box: RecBox<T>): T

type T1 = Box<string>;
type T2 = Box<T1>;
type T3 = Box<T2>;
type T4 = Box<T3>;
type T5 = Box<T4>;
type T6 = Box<T5>;

declare let b1: Box<Box<Box<Box<Box<Box<string>>>>>>;
declare let b2: T6;
declare let b3: InfBox<string>;
declare let b4: { value: { value: { value: typeof b4 }}};

unbox(b1); // string
unbox(b2); // string
unbox(b3); // InfBox<string>
unbox({ value: { value: { value: { value: { value: { value: 5 }}}}}}); // number
unbox(b4); // { value: { value: typeof b4 }}
unbox({ value: { value: { get value() { return this; } }}}); // { readonly value: ... }

// Inference from nested instantiations of same generic types

type Box1<T> = { value: T };
Expand Down