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Sign upfix(core): make QueryList implement Iterable in the type system #33536
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@alxhub should this change be included in patch branch as well? Thank you. |
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LGTM! This would allow me to remove quite a number of |
| // there) and this declaration is left here to ensure that TypeScript considers QueryList to | ||
| // implement the Iterable interface. This is required for template type-checking of NgFor loops | ||
| // over QueryLists to work correctly, since QueryList must be assignable to NgIterable. | ||
| [Symbol.iterator] !: () => Iterator<T>; |
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Splaktar
Nov 3, 2019
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Very interesting! For anyone else not completely familiar with using TypeScript Symbols to define class members, here's the docs: https://www.typescriptlang.org/docs/handbook/symbols.html
Originally, QueryList implemented Iterable and provided a Symbol.iterator on its prototype. This caused issues with tree-shaking, so QueryList was refactored and the Symbol.iterator added in its constructor instead. As part of this change, QueryList no longer implemented Iterable directly. Unfortunately, this meant that QueryList was no longer assignable to Iterable or, consequently, NgIterable. NgIterable is used for NgFor's input, so this meant that QueryList was not usable (in a type sense) for NgFor iteration. View Engine's template type checking would not catch this, but Ivy's did. As a fix, this commit adds the declaration (but not the implementation) of the Symbol.iterator function back to QueryList. This has no runtime effect, so it doesn't affect tree-shaking of QueryList, but it ensures that QueryList is assignable to NgIterable and thus usable with NgFor. Fixes #29842
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Originally, QueryList implemented Iterable and provided a Symbol.iterator on its prototype. This caused issues with tree-shaking, so QueryList was refactored and the Symbol.iterator added in its constructor instead. As part of this change, QueryList no longer implemented Iterable directly. Unfortunately, this meant that QueryList was no longer assignable to Iterable or, consequently, NgIterable. NgIterable is used for NgFor's input, so this meant that QueryList was not usable (in a type sense) for NgFor iteration. View Engine's template type checking would not catch this, but Ivy's did. As a fix, this commit adds the declaration (but not the implementation) of the Symbol.iterator function back to QueryList. This has no runtime effect, so it doesn't affect tree-shaking of QueryList, but it ensures that QueryList is assignable to NgIterable and thus usable with NgFor. Fixes #29842 PR Close #33536
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alxhub commentedNov 1, 2019
Originally, QueryList implemented Iterable and provided a Symbol.iterator
on its prototype. This caused issues with tree-shaking, so QueryList was
refactored and the Symbol.iterator added in its constructor instead. As
part of this change, QueryList no longer implemented Iterable directly.
Unfortunately, this meant that QueryList was no longer assignable to
Iterable or, consequently, NgIterable. NgIterable is used for NgFor's input,
so this meant that QueryList was not usable (in a type sense) for NgFor
iteration. View Engine's template type checking would not catch this, but
Ivy's did.
As a fix, this commit adds the declaration (but not the implementation) of
the Symbol.iterator function back to QueryList. This has no runtime effect,
so it doesn't affect tree-shaking of QueryList, but it ensures that
QueryList is assignable to NgIterable and thus usable with NgFor.
Fixes #29842