fp-option-ref · fp-ts Option 速查参考

作者提供的示例，实际效果取决于你的输入和使用工具。

输入

把这段多层可选属性访问改写成 fp-ts Option 管道，并给出默认值处理。

输出

预期交付：Option 相关函数用法与管道组合示例代码。（编辑说明，非实际运行结果）

---
name: fp-option-ref
description: Quick reference for Option type. Use when user needs to handle nullable values, optional data, or wants to avoid null checks.
risk: none
source: community
date_added: "2026-03-06"
version: 1.0.0
tags: [fp-ts, option, nullable, maybe, quick-reference]
---

# Option Quick Reference

Option = value that might not exist. `Some(value)` or `None`.

## When to Use
- You need a quick fp-ts reference for nullable or optional values.
- The task involves eliminating null checks, safe property access, or optional chaining with `Option`.
- You want a short reference card rather than a full migration guide.

## Create

```typescript
import * as O from 'fp-ts/Option'

O.some(5)              // Some(5)
O.none                 // None
O.fromNullable(x)      // null/undefined → None, else Some(x)
O.fromPredicate((n: number) => n > 0)(x) // false → None, true → Some(x)
```

## Transform

```typescript
O.map(fn)              // Transform inner value
O.flatMap(fn)          // Chain Options (fn returns Option)
O.filter(predicate)    // None if predicate false
```

## Extract

```typescript
O.getOrElse(() => fallbackValue)  // Get value or default
O.toNullable(opt)           // Back to T | null
O.toUndefined(opt)          // Back to T | undefined
O.match(onNone, onSome)     // Pattern match
```

## Common Patterns

```typescript
import { pipe } from 'fp-ts/function'
import * as O from 'fp-ts/Option'

// Safe property access
pipe(
  O.fromNullable(user),
  O.flatMap(u => O.fromNullable(u.profile)),
  O.flatMap(p => O.fromNullable(p.avatar)),
  O.getOrElse(() => '/default-avatar.png')
)

// Array first element
import * as A from 'fp-ts/Array'
pipe(
  users,
  A.head,  // Option<User>
  O.map(u => u.name),
  O.getOrElse(() => 'No users')
)
```

## vs Nullable

```typescript
// Nullable: concise and safe for a short access chain
const name = user?.profile?.name ?? 'Guest'

// Option: explicit and composable across multiple operations
pipe(
  O.fromNullable(user),
  O.flatMap(u => O.fromNullable(u.profile)),
  O.flatMap(p => O.fromNullable(p.name)),
  O.getOrElse(() => 'Guest')
)
```

Use Option when you need to **chain** operations on optional values.

## Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

## Reference scope

These are fp-ts 2.x fragments. Supply application variables, types, validators and imports, and check the installed version. `map` does not catch thrown exceptions. `Task` has no typed error channel; an improperly wrapped promise can still reject. Use `tryCatch` at fallible boundaries.

Official API: [fp-ts modules](https://gcanti.github.io/fp-ts/modules/).

先看看示例

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方法说明