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Jun 28, 2019
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docs(eslint-plugin): Expand docs for array-type #634

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docs(eslint-plugin): Expand docs for array-type
bradzacher Jun 21, 2019
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Merge branch 'master' into array-type-docs
bradzacher Jun 28, 2019
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88 changes: 69 additions & 19 deletions packages/eslint-plugin/docs/rules/array-type.md
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# Requires using either `T[]` or `Array<T>` for arrays (array-type)

```ts
class Foo<T = Array<Array<Bar>>> extends Bar<T, Array<T>>
implements Baz<Array<T>> {
private s: Array<T>;

constructor(p: Array<T>) {
return new Array();
}
}
```
Using the same style for array definitions across your codebase makes it easier for your developers to read and understand the types.

## Rule Details

This rule aims to standardise usage of array.
This rule aims to standardise usage of array types within your codebase.

## Options

Default config:
This rule accepts one option - a single string

- `"array"` enforces use of `T[]` for all types `T`.
- `"generic"` enforces use of `Array<T>` for all types `T`.
- `"array-simple"` enforces use of `T[]` if `T` is a simple type.

Without providing an option, by default the rule will enforce `"array"`.

### `"array"`

Always use `T[]` or `readonly T[]` for all array types.

Incorrect code for `"array"`:

```ts
const x: Array<string> = ["a", "b"];
const y: ReadonlyArray<string> = ["a", "b"];
```

```JSON
{
"array-type": ["error", "array"]
}
Correct code for `"array"`:

```ts
const x: string[] = ["a", "b"];
const y: readonly string[] = ["a", "b"];
```

- `array` enforces use of `T[]` for all types `T`.
- `generic` enforces use of `Array<T>` for all types `T`.
- `array-simple` enforces use of `T[]` if `T` is a simple type.
### `"generic"`

Always use `Array<T>` or `ReadonlyArray<T>` for all array types.

Incorrect code for `"generic"`:

```ts
const x: string[] = ["a", "b"];
const y: readonly string[] = ["a", "b"];
```

Correct code for `"generic"`:

```ts
const x: Array<string> = ["a", "b"];
const y: ReadonlyArray<string> = ["a", "b"];
```

### `"array-simple"`

Use `T[]` or `readonly T[]` for simple types (i.e. types which are just primitive names or type references).
Use `Array<T>` or `ReadonlyArray<T>` for all other types (union types, intersection types, object types, function types, etc).

Incorrect code for `"array-simple"`:

```ts
const a: (string | number)[] = ["a", "b"];
const b: ({ prop: string })[] = [{ prop: "a" }];
const c: (() => void)[] = [() => {}];
const d: Array<MyType> = ["a", "b"];
const e: Array<string> = ["a", "b"];
const f: ReadonlyArray<string> = ["a", "b"];
```

Correct code for `"array-simple"`:

```ts
const a: Array<string | number> = ["a", "b"];
const b: Array<{ prop: string }> = [{ prop: "a" }];
const c: Array<() => void> = [() => {}];
const d: MyType[] = ["a", "b"];
const e: string[] = ["a", "b"];
const f: readonly string[] = ["a", "b"];
```

## Related to

Expand Down