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# functional/prefer-tacit

📝 Replaces `x => f(x)` with just `f`.

⚠️ This rule _warns_ in the 🎨 `stylistic` config.

💡 This rule is manually fixable by [editor suggestions](https://eslint.org/docs/latest/use/core-concepts#rule-suggestions).

💭 This rule requires [type information](https://typescript-eslint.io/linting/typed-linting).

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This rule enforces using functions directly if they can be without wrapping them.

## Rule Details

If a function can be used directly without being in a callback wrapper, then it's generally better to use it directly.
Extra inline lambdas can slow the runtime down.

⚠️ Warning ⚠️: Use with caution as if not all parameters should be passed to the function, a wrapper function is then required.

### ❌ Incorrect

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```ts
/* eslint functional/prefer-tacit: "error" */

function f(x) {
  return x + 1;
}

const foo = [1, 2, 3].map((x) => f(x));
```

### ✅ Correct

```ts
/* eslint functional/prefer-tacit: "error" */

function f(x) {
  return x + 1;
}

const foo = [1, 2, 3].map(f);

const bar = { f };
const baz = [1, 2, 3].map((x) => bar.f(x)); // Allowed unless using `checkMemberExpressions`
```

## Options

This rule accepts an options object of the following type:

```ts
type Options = {
  checkMemberExpressions: boolean;
};
```

### Default Options

```ts
type Options = {
  checkMemberExpressions: false;
};
```

### `checkMemberExpressions`

If `true`, calls of member expressions are checked as well.
If `false`, only calls of identifiers are checked.

#### ❌ Incorrect

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```ts
/* eslint functional/prefer-tacit: ["error", { "checkMemberExpressions": true }] */

const bar = {
  f(x) {
    return x + 1;
  },
};

const foo = [1, 2, 3].map((x) => bar.f(x));
```

#### ✅ Correct

```ts
/* eslint functional/prefer-tacit: ["error", { "checkMemberExpressions": true }] */

const bar = {
  f(x) {
    return x + 1;
  },
};

const foo = [1, 2, 3].map(bar.f.bind(bar));
```