本篇同步發文於個人網站: Moving Features

This article references the chapter 8 " Moving Features " of Refactoring: Improving the Design of Existing Code (2nd Edition). Author had highlighted many important refactorings in this chapter.

I use .NET C# to practice with these refactorings and upload to Github.

(Photo from Pixabay: https://pixabay.com/illustrations/plumber-repair-tools-pipe-plunger-4427401/https://pixabay.com/illustrations/moving-boxes-mover-moving-truck-3671446/ )

Move Function

Tips

• If a nested function of a outer function may be used for other situations, move this nested function to a general scope.
• If a function of a class is better for other class, move this function into the target class.

Examples:

• Moving a Nested Function to Top Level
• Moving between Classes

Github

Move Field

Tips

• If other structures are modified after one field is modified, we should move this field into a central structure.
• Field should be encapsulated, it means that we add get/set accessors to encapsulate fields to avoid "Bare" record.

Examples:

• A simple example
• Moving to a Shared Object

Github

Move Statements into Function

Tips

• If some statement repeatably works on many places, we should move it into a function.

Examples:

• A simple example

Github

Move Statements into Callers

Tips

• If some statement are changed by callers in a function, we should extract it to each caller.

Examples:

• Just use the Move Statements into Function example from end to start

Replace Inline Code with Function Call

Tips

• If some inline code has been implements in some function, replace it with the function.
• A good naming function shows what the inline code outputs without understanding the implementation

Examples:

// before refactoring
bool hasMyFavoriteFruit = false;
foreach(var fruit in basket)
{
    if(fruit == "Apple")
    {
        hasMyFavoriteFruit  = true;
    }
}

// after refactoring
bool hasMyFavoriteFruit = basket.Contains("Apple");

Slide Statements

Tips

• Some variable declarations are placed together on the top of scope, but author recommends that he declares variable when only first time he uses it.
• Some statement has side-effect. If we slide it without test, it may cause the error.
• We can implement the statement (function) by using Command/Query separation pattern to avoid the side-effect.
• This refactoring focuses on the change of the state. When we slide statement, Split Variable is a good method.

Examples:

Sliding with Conditionals

// before refactoring
Response result = null;
if(connection.Status == Status.OK)
{
    result = CreateSuccessMessage();
    connectionResponses.Add(result);
}
else
{
    result = CreateFailsMessage();
    connectionResponses.Add(result);
}

return result;

// after refactoring
Response result = null;
if(connection.Status == Status.OK)
{
    result = CreateSuccessMessage();
}
else
{
    result = CreateFailsMessage();
}

connectionResponses.Add(result);
return result;

Split Loop

Tips

• If a loop contains many independent works, split them into their own loop scope.
• We use Move Statement to move related variable declaration near by the new loop.
• Split loop can be extracted as a function.
• Replace Loop with Pipeline is a better implementation.

Examples:

• A simple example

Github

Replace Loop with Pipeline

Tips

• Collection Pipeline is a modern pattern. A pipeline receives a collection and process it with some operations and outputs a new collection.
• JavaScript has map/filter/... pipeline functions, C# has LINQ (select/where...).
• Pipeline increases the code readability.

Examples:

• A simple example

Github

Remove Dead Code

Tips

• If some code is not used ever, remove it to avoid confusing you/your team members.
• Version control can manage all code history. Make the good use of it.

Conclusion

This chapter introduces me how to move the code logic greatly. In my early coding job, I used to write long logic function. And this function was gradually hard maintainable. I learned some like Moving Features skills to enhance the code but it still was not completed. I have grown up to write better code when I study this refactoring chapter. If you want to learn detailed motivation and mechanics, study the chapter 8 " Moving Features " of Refactoring: Improving the Design of Existing Code (2nd Edition). and it improves our programmer's ability.