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Sometimes you want to customize JSON encoding and decoding of a type in this lecture.

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We're going to take a look at the Marshaler and Unmarshaler interfaces.

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Let's get started.

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Here I want to encode the list value into
this JSON data (on the right).

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First of all I'm going to encode the list into JSON using marshal indent

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it's going to give me the encoding result as a data bytes slice I'm going to save them into variables.

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Then to check for the error.

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And lastly I'm going to print out the encoded data.

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OK before going on further I want to talk about something here.

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I used the fatal function.

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This function is equals to first printing the error message and then calling the os exit function.

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So this is kind of equals to printing the message first and then terminating from the program.

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Okay.

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So by using this function I don't have to type these two lines of code.

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Okay let's give it a try.

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Hmm.

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It didn't print anything it's because product doesn't export any of its fields.

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So I need to export all of these fields like so their first letters are uppercase now.

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So there should be other problems on the other side of the code.

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So I'm going to take a look at them.

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There are some problems in the list type so I'm going to change these letters to uppercase as well.

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And there are also other problems in the main function I'm gonna change these field names into uppercase.

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Great.

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Now let's give it another try.

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Nice.

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Now it encodes the list into this JSON data however I don't want the release dates to be printed to

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be encoded like this.

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I want them to be integers—to be timestamp values.

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So how can I do that to do that.

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I need to use an interface.

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Let me show you its documentation.

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So if I implement this method on the Timestamp Type I can customize the behavior of the JSON encoder.

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So I'm going to copy this method from here and paste it into the timestamp type and I'm going to attach

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it to the timestamp like this and lastly I'm going to change these result values into named result

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values because I'm going to use this byte slice inside of the function and I'm going to keep the error

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all right here.

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First I need to convert this timestamp into an integer and then I need to put that integer into the

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data slice.

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OK to do that there are two functions.

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The first one is the Unix function which returns us an integer and there is also a strconv append

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int function.

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This function takes a bytes slice and an integer number.

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This should be the ts which is an integer which will be an integer.

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And then lastly I'm going to give it the decimal based system which is 10.

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So let me copy this from here and put it here.

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And for the integer part I'm going to call the Unix method of the timestamp.

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Remember the timestamp is a time value.

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Right.

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So that's why I can call this method here.

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So it's gonna return me the timestamp as an integer value.

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OK.

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Now I need to return it first because this append int function returns us a byte slice and then

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I'm going to return a nil error because there is no error.

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OK.

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So by doing this I am customizing the behavior of this encoder.

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This is the encoder.

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OK let me try this.

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Great.

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Now the timestamps are integers.

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Let me show you how does it work.

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Let's say there is a product value and I'm going to call the marshal indent function on the list value.

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This is one of the products inside of the list.

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So first it's going to encode the title and price fields and it's gonna use default encoding.

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But for the released field it's a timestamp.

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It has a Marshal JSON method.

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So the marshal indent function is gonna call this Marshal JSON method and the timestamp is going to

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do its own stuff and customize this encoding and then returns it as a byte slice to the Marshal indent

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function.

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So this way we can customize the behavior of the encoder or in other words the Marshaler

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not that you understand how to customize the encoding behavior.

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Now I'm going to show you how to customize the decoding behavior as well so to do that.

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I'm going to run this program once more here.

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I'm going to get this JSON data and I'm going to put it into a constant like so.

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Now I'm going to comment out this code and then I'm going to create a list value and I'm going to try

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to decode this JSON data into the list value.

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So to do that I'm going to call the JSON Unmarshal function.

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I'm going to pass the JSON data and the address of this list and then I'm going to handle the error

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like so.

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And lastly I'm going to print out the list that's it.

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Oops! I need to change this into a bytes slice.

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Okay.

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Now let me try it.

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It doesn't know how to convert these numeric timestamp values.

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We need to teach it how to do so.

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So I'm going to go to the timestamp type and I'm going to add another method here.

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But first let me show you its documentation all right.

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This unmarshaler interface can customize the behavior of decoding.

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OK.

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So I'm going to copy this method from here and I'm going to paste it here then I'm going to attach this

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method to the timestamp.

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OK let me give it a name to this byte slice as well.

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So here I'm going to get all of these values one by one into this method.

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So let's assume that I get this value OK here I need to set this timestamp receiver into this value

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but I need to do so as a timestamp value.

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Right now we're going to receive it as an integer value.

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So I need to convert this into a timestamp to do that.

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I'm going to call the timestamp function.

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I'm going to pass this data to the timestamp function like so I'm passing it as string value because the

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to timestamp function can only understand how to convert string values to timestamp values and lastly

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I'm going to change this into a pointer receiver so that I can change its original value like so.

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And lastly I'm going to return a nil error.

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OK let me try this.

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Great.

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Now it works.

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The unmarshall function decodes all of these timestamp values into a list value.

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All right.

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Congrats.

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That's all for now.

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I hope you enjoyed it so far.
If you want to take a look at this summary

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If you want to take a look at this summary
you can do so now.

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See you in the next lecture.

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Bye bye!