Скачать или смотреть How to Initialize Struct with Values from an Array of Interface in Go

Learn how to easily initialize a struct with values from an array of interface in Go. This guide provides a step-by-step explanation of the process and highlights common pitfalls.
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This video is based on the question https://stackoverflow.com/q/68030440/ asked by the user 'knn7713' ( https://stackoverflow.com/u/14176416/ ) and on the answer https://stackoverflow.com/a/68035511/ provided by the user 'Bracken' ( https://stackoverflow.com/u/1440786/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Initialize Struct with Values from an Array of Interface in Go

Working with data received from a server can sometimes be tricky, especially if you're relatively new to Go and dealing with interfaces. One common challenge is how to initialize a struct with values that are packed into an array of interfaces. In this guide, we will break down the process of converting data coming from a WebSocket into a well-defined struct.

Understanding the Problem

Imagine you receive a message from a server in the following format:

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This message is parsed into a []interface{} variable, making it difficult to directly map the values into a structured type like a struct. If you're trying to convert this array of interfaces into a more accessible format, you might run into type conversion errors, such as the Cannot convert an expression of the type 'interface{}' to the type 'int32'.

Initial Approach

Here is an example of the initial approach you might take:

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You then attempt to create a struct to hold the order details:

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The problem arises when you try to convert each item in the array into the appropriate type without any auxiliary functions, leading to multiple cumbersome switch cases or manual type assertions.

A Robust Solution: Using UnmarshalJSON

If you can ensure that the codec used on the WebSocket connection will always be JSON, a more elegant approach involves defining the struct and providing an UnmarshalJSON function. This function will help decode the incoming data directly into an instance of your struct.

Step-by-Step Implementation

Define the Order Struct

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Implement the UnmarshalJSON Function

The heart of the solution lies in customizing how the JSON data is unmarshalled:

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Receive Data and Populate the Struct

Finally, receive the data and automatically populate the struct:

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Conclusion

This approach considerably reduces the complexity involved in handling data from your WebSocket. By leveraging the UnmarshalJSON method, you can effortlessly map incoming JSON payloads from your server into meaningful Go structures that you can work with.

Remember, when designing APIs, it's best to avoid complex structures like mixed-type arrays. A more structured approach with clear types will make working with incoming data much simpler.

By following the steps outlined in this guide, you will be able to effectively initialize a struct from values in an array of interfaces in Go without facing the common pitfalls of type conversion.