Transform Return Type aka Wrap Return Value

Some tools have this, Resharper includes it in the “Transform Parameters” refactoring. IntelliJ has an additional plugin that offers to Wrap Return Value. If you don’t have those tools then these steps achieve the same thing with only ‘Extract Function’ and ‘Inline Function.’

Identify

Usually you want this refactoring when a method has multiple return values that and either you’re only getting one of them, or you’re putting them in an awkward collection type before returning them.

Prepare

I usually find this one goes easier if I inline the method first, unless it’s called from several places.

Implement

• Identify which local variables will be combined into the new wrapper type, eg var a; var b; var c;.
• Identify a position in the code after these local variables have all been declared and where you can create a new variable of the new type to wrap them.
• Pretend you already have the new class, declare a variable for it. Call its constructor with the arguments you want to put in the new type, eg var wrapper = ReturnTypeWrapper(a, b, c).
• Use your tools to create that class ReturnTypeWrapper.
• Store all the constructor arguments in public fields.
• change all the references to these variables to use the fields of your new class, eg a becomes wrapper.a. (Use search and replace within a selection).
• ‘Extract method’ on all the code that uses wrapper. The method should have the signature you wanted.

Clear

Try to remove the declaration of the local variables and instead use default values in the constructor of your new class.

Follow up

Look for other methods you could extract and move to the new type. Look for Feature Envy on its fields.

Prompted by Code Smells

• Primitive Obsession
• Variable with Long Scope

Relevant Learning Hours

Sources

• This refactoring was contributed to this site by Emily Bache

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