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Add test relating type predicates with and without this parameters

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This commit is contained in:
Anders Hejlsberg
2019-03-17 17:39:08 -10:00
parent 3dd0814069
commit b6aff98fd7
1 changed files with 27 additions and 0 deletions
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27
tests/cases/compiler/contravariantInferenceAndTypeGuard.ts Normal file
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// @strict: true
interface ListItem<TData> {
prev: ListItem<TData> | null;
next: ListItem<TData> | null;
data: TData;
}
type IteratorFn<TData, TResult, TContext = List<TData>> = (this: TContext, item: TData, node: ListItem<TData>, list: List<TData>) => TResult;
type FilterFn<TData, TResult extends TData, TContext = List<TData>> = (this: TContext, item: TData, node: ListItem<TData>, list: List<TData>) => item is TResult;
declare class List<TData> {
filter<TContext, TResult extends TData>(fn: FilterFn<TData, TResult, TContext>, context: TContext): List<TResult>;
filter<TResult extends TData>(fn: FilterFn<TData, TResult>): List<TResult>;
filter<TContext>(fn: IteratorFn<TData, boolean, TContext>, context: TContext): List<TData>;
filter(fn: IteratorFn<TData, boolean>): List<TData>;
}
interface Test {
a: string;
}
const list2 = new List<Test | null>();
const filter1 = list2.filter(function(item, node, list): item is Test {
this.b; // $ExpectType string
item; // $ExpectType Test | null
node; // $ExpectType ListItem<Test | null>
list; // $ExpectType List<Test | null>
return !!item;
}, {b: 'c'});
const x: List<Test> = filter1; // $ExpectType List<Test>