38626b0c08
Co-authored-by: Yassin Kammoun <52890329+yassin-kammoun-sonarsource@users.noreply.github.com>
64 lines
2.8 KiB
Plaintext
64 lines
2.8 KiB
Plaintext
== Why is this an issue?
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In TypeScript, intersections are used to combine multiple types into a single one. An intersection type is represented using the ampersand symbol ``++&++``. It allows you to combine multiple types into a single type that includes all the properties and methods from each type, thus creating more flexible and powerful type definitions.
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However, some of the basic types of TypeScript should not be used with intersections:
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* The `never` type represents the type of values that never occur. Intersecting any type with `never` will always result in type `never`.
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* The `any` type allows to opt-out of type checking during compilation. Expressions of type `any` allow you to access arbitrary properties, even ones that don't exist. `any` comes at the cost of losing type safety, which is one of the main motivations for using TypeScript. Avoid using `any` when not necessary. Intersecting any type with `any` will always result in type `any`.
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* The `undefined` and `null` types are the types for their respective value. Intersecting any type with them will always result in type `never`.
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* The `void` type implies the absence of a type. Intersecting any type with `void` will always result in type `never`.
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Additionally, an intersection with a type without members (for example, ``++{}++``) doesn't change the resulting type, is redundant, and can be safely removed from the intersection.
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[source,javascript,diff-id=1,diff-type=noncompliant]
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----
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type Foo = T & null; // Noncompliant: 'Foo' is always 'never'
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type Bar = T & any; // Noncompliant: 'Bar' is always 'any'
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type Baz = T & U & {}; // Noncompliant: '{}' has no members and is redundant
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----
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Use consistent types that accurately reflect the domain of values of the defined data type.
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[source,javascript,diff-id=1,diff-type=compliant]
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----
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type Foo = T | null;
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type Bar = T & U;
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type Baz = T & U;
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----
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== Resources
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=== Documentation
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* https://www.typescriptlang.org/docs/handbook/unions-and-intersections.html#intersection-types[TypeScript - Intersection Types]
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* https://www.typescriptlang.org/docs/handbook/basic-types.html#never[TypeScript - `never`]
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* https://www.typescriptlang.org/docs/handbook/basic-types.html#any[TypeScript - `any`]
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* https://www.typescriptlang.org/docs/handbook/basic-types.html#null-and-undefined[TypeScript - `null` and `undefined`]
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* https://www.typescriptlang.org/docs/handbook/basic-types.html#void[TypeScript - `void`]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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* Remove this type without members or change this type intersection.
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* Simplify this intersection as it always has type ["any" | "never"].
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=== Highlighting
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type without members or full intersection if it has ``++any++`` or ``++never++``
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endif::env-github,rspecator-view[]
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