《重构》 8. 搬移特性

## 8.1 搬移函数（Move Function）

**曾用名**：*搬移函数（Move Method）*

**重构前**：

```csharp
class Account
{
    decimal OverdraftCharge { get; }
}
```

**重构后**：

```csharp
class AccounType
{
    decimal OverdraftCharge { get; }
}
```

## 8.2 搬移字段（Move Field）

**重构前**：

```csharp
class Customer
{
    public Plan Plan { get; set; }
    public decimal DiscountRate { get; set; }
}
```

**重构后**：

```csharp
class Customer
{
    public Plan Plan { get; set; }
    public decimal DiscountRate
    {
        get
        {
            return Plan.DiscountRate;
        }
    }
}
```

## 8.3 搬移语句到函数（Move Statement into Function）

**反向重构**：*搬移语句到调用者（Move Statements to Caller）*

**重构前**：

```csharp
result.Add($"title: {aPerson.Photo.Title}");
result.AddRange(PhotoData(aPerson.Photo));

static string[] PhotoData(Photo aPhoto)
{
 return new string[] {
 $"location: {aPhoto.Location}",
 $"date: {aPhoto.Date:yyyy-MM-dd}",
 };
}
```

**重构后**：

```csharp
result.AddRange(PhotoData(aPerson.Photo));

static string[] PhotoData(Photo aPhoto)
{
 return new string[] {
 $"title: {aPhoto.Title}",
 $"location: {aPhoto.Location}",
 $"date: {aPhoto.Date:yyyy-MM-dd}",
 };
}
```

## 8.4 搬移语句到调用者（Move Statements to Callers）

**反向重构**：*搬移语句到函数（Move Statement into Function）*

**重构前**：

```csharp
EmitPhotoData(outStram, aPerson.Photo);

void EmitPhotoData(Stream outStram, Photo aPhoto)
{
 outStram.Write(Encoding.UTF8.GetBytes($"title: {aPhoto.Title}"));
 outStram.Write(Encoding.UTF8.GetBytes($"location: {aPhoto.Location}"));
}
```

**重构后**：

```csharp
EmitPhotoData(outStram, aPerson.Photo);
outStram.Write(Encoding.UTF8.GetBytes($"location: {aPerson.Photo.Location}"));

void EmitPhotoData(Stream outStram, Photo aPhoto)
{
 outStram.Write(Encoding.UTF8.GetBytes($"title: {aPhoto.Title}"));
}
```

## 8.5 以函数调用取代内联代码（Replace Inline Code with Function Call）

**重构前**：

```csharp
var appliesToMass = false;
foreach (var s in states)
{
    if (s == "MA")
    {
        appliesToMass = true;
    }
}
```

**重构后**：

```csharp
var appliesToMass = states.Contains("MA");
```

## 8.6 移动语句（Slide Statements）

**曾用名**：*合并重复的代码片段（Consolidate Duplicate Conditional Fragments）*

**重构前**：

```csharp
var pricingPlan = RetrievePricingPlan();
var order = RetreiveOrder();
decimal charge;
var chargePerUnit = pricingPlan.Unit;
```

**重构后**：

```csharp
var pricingPlan = RetrievePricingPlan();
var chargePerUnit = pricingPlan.Unit;
var order = RetreiveOrder();
decimal charge;
```

## 8.7 拆分循环（Split Loop）

**重构前**：

```csharp
var averageAge = 0;
var totalSalary = 0;
foreach (var p in people)
{
    averageAge += p.Age;
    totalSalary += p.Salary;
}
averageAge = averageAge / people.Length;
```

**重构后**：

```csharp
var totalSalary = 0;
foreach (var p in people)
{
    totalSalary += p.Salary;
}

var averageAge = 0;
foreach (var p in people)
{
    totalSalary += p.Salary;
}
averageAge = averageAge / people.Length;
```

一般在拆分循环后，会考虑对每个循环应用别的重构手法，如提炼函数等

## 8.8 以管道取代循环（Replace Loop with Pipeline）

**重构前**：

```csharp
var names = new List<string>();
foreach (var i in input)
{
 if (i.Job == "programmer")
 {
 names.Add(i.Name);
 }
}
```

**重构后**：

```csharp
var names = input.Where(i => i.Job == "programmer").Select(i => i.Name).ToList();
```

## 8.9 移除死代码（Remove Dead Code）

**重构前**：

```csharp
if (false)
{
    doSomethingThatUsedToMatter();
}
```

**重构后**：

```csharp
// do nothing
```

## 附1. 引用

1. [《重构：改善既有代码的设计》][1] -- 马丁·福勒（*Martin Fowler*）

[1]: https://union-click.jd.com/jdc?e=&p=AyIGZRhaEwAQBFUZXBIyEgRREl4QChs3EUQDS10iXhBeGlcJDBkNXg9JHU4YDk5ER1xOGRNLGEEcVV8BXURFUFdfC0RVU1JRUy1OVxUBFg5QHlMcMloDXR8JHXtmYiNlWEBFeV1UUjxnS0QLWStaJQITBlYbXB0LFQJlK1sSMkBpja3tzaejG4Gx1MCKhTdUK1sRCxQBVxtdFAcTB1crXBULIloNXwZBXUReEStrJQEiN2UbaxYyUGlUE1xGBhFQBR5bFVUXVAdOU0dWGwFdTwtAAkZTVE9fRTIQBlQfUg%3D%3D (《重构：改善既有代码的设计》)

《重构》 8. 搬移特性

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