WEBVTT

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Welcome.

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Now it's time to talk about append function in detail.

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All right let's get started.

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Let's see how it works.

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First you need to type append then you need to pass it a slice value.

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And lastly you need to pass it an element. In this most basic form append just append

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the elements to the given slice and then it returns a new slice value with the newly appended element

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like the len function

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The append function is also a built in function. So it can be used everywhere without importing any package.

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The append function is also a built in function. So it can be used everywhere without importing any package.

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OK let's take a look at an example. Let's create a new slice using a slice literal like this.

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The slice literal is just like an array literal but without a length.

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So it creates a slice with three elements right from the start.

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So its length becomes 3. Let's append a new element to this slice. After the append the slice stays

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the same.

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So nothing happens.

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Let me show you why. Behind the scenes the append function creates a new slice value.

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And it appends the new element to the new slice. It's because the append cannot change the original slice.

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So instead it returns a new slice.

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That is why the original slice stays the same.

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We need to use the new slice instead.

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Let's do that.

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Here, I'm saving the new slice to the nums slice.

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But doing so may look weird to you.

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When go into deeper into slices,

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I'll talk about why we usually do so later.

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Now let's get back to the code. Since I've fixed the code

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let's try it one more time. Now it works.

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We've got a bigger slice now with four elements.

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Okay let's add one more element to the new slice

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Now it has five elements so its length becomes five. The append function adds the new elements by looking

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at the length of a slice. For example, it appends 4 right after 3 because of the slice's length was 3

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It appends 9 right after 4 because the slice's length was 4. By the way you don't need to call

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the append function multiple times, there is an easier way. Let me show you. As you can see you can also

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append multiple elements like this. I've just separated them using commas. This way you can call the append

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only once. You can do so because the append function is a variadic function, so it can accept dynamic number

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of arguments. So you can add as many elements as you want.

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There is one more syntax by the way: it's called the ellipses; it allows you to append a slice to another slice.

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Let me show you. Let's say there is also another slice like this. To append this green slice to the nums slice.

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I just need to type it like this. The ellipses operator takes the tens slice here and sends its elements

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as arguments to the append function.

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So when I run this it appends all the elements of tens slice to the back of the nums slice, and

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it returns a larger slice with a length of 5. As you can see this code works as if I'm passing the

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arguments manually to the append function like this.

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OK let's take a look at an example in the coding editor.

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let's say I want to create a todo list and I don't know how many tasks that I'm going to store in that

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list.

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So I need a data structure that can grow indefinitely.

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So it's a good use case for a slice.

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Each one of my tasks is a string value so I'm going to declare a new string slice called the todo

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like this.

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By the way in this section I'm going to use a special library that I've created.

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So it will be very easy easier for you to understand what's going on behind the scenes.

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However you don't have to use my library.

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You can also use a fmt.Println or fmt.Printf. They will all work the same.

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OK.

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So first of all let's get my library using the go get command like this. Cool!

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Let me import it. I'm going to change its name to "s" to keep it short in the code okay.

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By the way for the rest of this section when I don't explain it, please always import the pretty slice

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package like this.

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Okay? My package has a Show function, you can pass it a message and an arbitrary number of slices.

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So my function is also a variadic function like the append function.

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All right let me show you the todo slice. As you can see the first argument is displayed in here as todo.

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, and it just prints nil slice here because a slice doesn't contain any items yet it's a nil slice.

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So let's add a new item to the slice here I'm overriding the to do slice variable with the new slice

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value.

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So behind the scenes the old sliced value disappears.

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Let me run it. Now the to do slice contains the new element so its length becomes 1.

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It is a larger slice than before.

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So always remember the append function returns you a new slice value, so you need to save it over your

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original slice or the return slice value will be lost. By the way,

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here, todo slice's element type is string, right?

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So you can only append string values to this slice.

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For example let me try append an integer like this, as you can see doesn't work so, this means that you

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can only append the same type of elements to a slice. All right!

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Now let me add three more elements. All right!

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Let me run it. Cool, now the slice contains 4 elements so its length is 4 now.

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I'll explain the cap and ptr here later by the way.

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Don't worry about down for now.

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My package also shows the index positions of the elements inside the slice.

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For example "sing" is at the 0 index and "code" is at the 2 index.

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Okay as an example let me get the 3rd element like this.

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It just prints code, anyway.

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Let me remove this okay.

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By the way as I said I can also add multiple items using the append function.

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Let me show you. OK. Cool! It's the same output as before, right?

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By the way as I showed you before I can also append a slice.

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For example let's say I have two todos for tomorrow like this.

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Now I'm going to append them to the todo slice like so. OK, let me run it.

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As you can see the append function appends the tomorrow slices' elements to the todo slice.

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Cool.

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As I told you, behind the scenes passing a slice value to the append function almost looks like this. All right.

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That's all for now.

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See you in the next lecture. Bye bye!