Why do I have to use an address when passing pointers in Go? What are the requirements for the UnmarshalKey function of the Viper library?

Detailed explanation of Go language pointer and Viper library UnmarshalKey function and answers to the questions

This article explores the Go language pointer syntax and the use of the Viper library UnmarshalKey function, and explains why addressable pointers must be passed when using UnmarshalKey .

Go language pointer:

The memory address of the pointer in Go language stores the variable. Use the & operator to get the address of the variable and use the * operator to access the value of the variable pointed to by the pointer. The pointer type is declared as *类型名, for example, *int represents a pointer to an integer.

Viper library UnmarshalKey function:

The Viper library is used to read and manage configurations, and the UnmarshalKey function deserializes specific key-value pairs in the configuration into a Go structure. The key point is that UnmarshalKey function requires that the target structure must be addressable, which means that the pointer of the structure must be passed, not the structure itself. This is because UnmarshalKey needs to modify the values ​​in the structure, and only the pointer can point to the modifyable memory location.

Code examples and problem analysis:

In the provided code, global.serversetting is already a pointer to the serversettings structure. However, when setting.readsection("server", global.serversetting) is called in the main function, the pointer global.serversetting itself is passed, not the address of the pointer. The UnmarshalKey function needs a pointer to this pointer in order to modify the structure it points to.

Therefore, the reason for result must be addressable (a pointer) error is that although global.serversetting is a pointer, it is not an addressable memory location and cannot be modified directly by UnmarshalKey . We need to pass its address &global.serversetting so that the UnmarshalKey function can modify the serversettings structure pointed to by global.serversetting .

Code correction:

Modify the code in main function to:

 setting.readsection("server", &global.serversetting)

In this way, &global.serversetting passes the address of the global.serversetting pointer, which meets the requirements of the UnmarshalKey function for addressable pointers.

Summarize:

The UnmarshalKey function requires an addressable pointer as a parameter in order to modify the structure data it points to. Even if the variable itself is a pointer, its address must be passed (using the & operator) to meet this requirement. Understanding the concepts of Go pointers and addressability is crucial to the correct use of Viper libraries.

(Image description: A simple Go language pointer diagram showing how pointer variables store memory addresses)

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