"Extract Function" from block of code

[scriptnull]

I am not sure if this feature already exists, but as far as I have researched, I am not able to find.

I remember seeing this feature used significantly in Visual Studio while writing C# by almost every .NET programmer, I have come across. I am surprised, that I am not able to find it in VS code.

Let's say I have a something like

package arrays

import "testing"

func TestNewBitArray(t *testing.T) {
	var size int64 = 1
	a := NewBitArray(size)
	bArray := []int8(a)
	if len(bArray) != 1 {
		t.Error("Expected length to be 1, but got", len(bArray))
	}

	size = 10
	a = NewBitArray(size)
	bArray = []int8(a)
	if len(bArray) != 2 {
		t.Error("Expected length to be 2, but got", len(bArray))
	}

	size = 32
	a = NewBitArray(size)
	bArray = []int8(a)
	if len(bArray) != 4 {
		t.Error("Expected length to be 4, but got", len(bArray))
	}
}

There are repeated blocks of instructions the code, which someone might prefer writing during the initial phase of development. After things start to work, I would typically want to make a function out of the repeated block and use it.

Now the workflow would be, I would select the repeated code block. In my case,

	a := NewBitArray(size)
	bArray := []int8(a)
	if len(bArray) != 1 {
		t.Error("Expected length to be 1, but got", len(bArray))
	}

and execute the command called "Extract Function" from context menu or from cmd+p or from "Go" Menu.

This would result in generating functions with appropriate method signature.

	var checkSizeClosure = func(size int) {
		a := NewBitArray(size)
		bArray := []int8(a)
		if len(bArray) != 1 {
			t.Error("Expected length to be 1, but got", len(bArray))
		}
	}

or

func checkSizeLocal(t *testing.T, size int) {
	a := NewBitArray(size)
	bArray := []int8(a)
	if len(bArray) != 1 {
		t.Error("Expected length to be 1, but got", len(bArray))
	}
}

With the newly generated function, I can tweak it a little bit to add an expected variable and my tests could be refactored into an idiomatic table based golang tests like this

package arrays

import "testing"

func TestNewBitArray(t *testing.T) {
	cases := []struct {
		input    int
		expected int
	}{
		{1, 1}, {10, 2}, {32, 4},
	}

	checkSize := func(size, expected int) {
		a := NewBitArray(size)
		bArray := []int8(a)
		if len(bArray) != expected {
			t.Errorf("Expected length to be %d, but got %d", expected, len(bArray))
		}
	}

	for _, testCase := range cases {
		checkSize(testCase.input, testCase.expected)
	}
}

Having "Extract Function" feature would help much in cleaning the code base that is full of repeated code.

[ramya-rao-a]

Yes, this would be a cool feature indeed.
#588 was logged to track this.
Closing this issue in favor of #588

PRs are welcome

[ramya-rao-a]

The latest beta version (0.9.3-beta.2) of this extension has this feature. Please see Refactoring in VS Code on how you can use the refactor feature.