3 ms·

Tell me few .. to me types were useful for hinting in ide but vscode already gives good hints

simplify 7y ago
Types are not just for autocompleting, but also for making illegal states unrepresentable[0]. For example, let's say you have Question model with two types: MultipleChoice and ShortAnswer. In TypeScript you can model it like this: type MultipleChoice = { mode: 'mc' body: string choices: string[] expectedAnswer: number } type ShortAnswer = { mode: 'sa' body: string exampleAnswer: string } type Question = MultipleChoice | ShortAnswer TypeScript's compiler will then enforce data structure consistency across your entire codebase. For example, if you were rendering a question in React: type Props = { question: Question } const MyComponent = (props: Props) => { props.question.body // Ok, since all questions have a body props.question.choices // Type error, since only MC has choices if (props.question.mode === 'mc') { props.question.choices // Ok now, since we checked the mode of question } } You can also use these types to force certain code to always be correct. For example, if you wanted to display a human-readable version of a Question's mode, you could write: const prettyQuestionType: Record<Question["mode"], string> = { mc: 'Multiple Choice', sa: 'Short Answer', } and now TypeScript will force prettyQuestionType to contain keys for all modes. That includes when you add a new Question mode later. Once you learn how to lean on the type checker, you think less about such details, and your mind becomes freer to think at a higher level, increasing your overall productivity. There is a learning curve though, so be aware. [0] https://fsharpforfunandprofit.com/posts/designing-with-types-making-illegal-states-unrepresentable/ https://fsharpforfunandprofit.com/posts/designing-with-types...
- techsin101 7y ago
  this indeed looks useful. so you can give multiple types by using '|' ? and if there is vagueness compiler will let you know.. mind blown.

Types are not just for autocompleting, but also for making illegal states unrepresentable[0]. For example, let's say you have Question model with two types: MultipleChoice and ShortAnswer. In TypeScript you can model it like this: type MultipleChoice = { mode: 'mc' body: string choices: string[] expectedAnswer: number } type ShortAnswer = { mode: 'sa' body: string exampleAnswer: string } type Question = MultipleChoice | ShortAnswer TypeScript's compiler will then enforce data structure consistency across your entire codebase. For example, if you were rendering a question in React: type Props = { question: Question } const MyComponent = (props: Props) => { props.question.body // Ok, since all questions have a body props.question.choices // Type error, since only MC has choices if (props.question.mode === 'mc') { props.question.choices // Ok now, since we checked the mode of question } } You can also use these types to force certain code to always be correct. For example, if you wanted to display a human-readable version of a Question's mode, you could write: const prettyQuestionType: Record<Question["mode"], string> = { mc: 'Multiple Choice', sa: 'Short Answer', } and now TypeScript will force prettyQuestionType to contain keys for all modes. That includes when you add a new Question mode later. Once you learn how to lean on the type checker, you think less about such details, and your mind becomes freer to think at a higher level, increasing your overall productivity. There is a learning curve though, so be aware. [0] https://fsharpforfunandprofit.com/posts/designing-with-types-making-illegal-states-unrepresentable/ https://fsharpforfunandprofit.com/posts/designing-with-types...

techsin101 7y ago
this indeed looks useful. so you can give multiple types by using '|' ? and if there is vagueness compiler will let you know.. mind blown.