Avoid calling indexOf when checking array element types
#18619
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Love the reference! Do we believe this fixes #17051? |
DanielRosenwasser
requested changes
Sep 21, 2017
src/compiler/checker.ts
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| case SyntaxKind.ArrayLiteralExpression: { | ||
| const arrayLiteral = <ArrayLiteralExpression>parent; | ||
| const type = getApparentTypeOfContextualType(arrayLiteral); | ||
| return getContextualTypeForElementExpression(type, indexOf(arrayLiteral.elements, node)); |
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If you want to ensure you're always searching pretty efficiently, you can do a binary search using the pos of the node.
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Sent #18635 as a PR to this branch.
DanielRosenwasser
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Sep 21, 2017
ghost
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Shlemiel gets a job as a type checker, checking the contextual types of array elements. On the first day he takes his array contextual type out to the AST and finishes 300 elements of the array. "That's pretty good!" says his boss, "you're a fast worker!" and pays him a kopeck.
The next day Shlemiel only checks 150 elements. "Well, that's not nearly as good as yesterday, but you're still a fast worker. 150 elements is respectable," and pays him a kopeck.
The next day Shlemiel checks 30 elements of the array. "Only 30!" shouts his boss. "That's unacceptable! On the first day you did ten times that much work! What's going on?"
"I can't help it," says Shlemiel. "Every day I get farther and farther away from the beginning of the array!"
indexOfwas causing us to take ever-increasing time when for every array element, we would start counting again from the beginning of the array to find our position. (This only happens if the array has a contextual type.) This is an instance of a general problem where we climb ancestors to recompute information instead of passing it down directly.I ran the performance tests and saw no negative effect on checker time, probably because our tests don't use lots of long arrays.