How to Safely Convert Between Slices of Structs in Go: A Guide to Type Conversion and Best Practices

Type Conversion between Slices of Structs in Go

When working with slices of structs in Go, it is important to understand the differences between various types. In this case, we have the following types:

• ListSociete: A custom struct type used for storing a list of Societe structs.
• []Societe: A slice of Societe structs.
• []struct{Name string json:"a.name"}: An anonymous struct type with a single field Name and a JSON tag.

Question 1: Are []struct{Name string} and []struct{Name string json:"a.name" } different?

Yes, they are different because of the JSON tag json:"a.name". The Go specifications clearly state that two struct types are identical only if they have the same fields, names, types, and tags.

Question 2: Is ListSociete different from []struct{Name string}?

Yes, they are different because ListSociete is a custom type while []struct{Name string} is an anonymous type. They also have different field names.

_Solution:

There are two options for converting between these types:

Option 1: Copy through Iteration

This method is safe and reliable, but requires explicit copying:

<code class="go">ls := make(ListSociete, len(res))
for i := 0; i < len(res); i++ {
    ls[i].Name = res[i].Name
}
return ls, nil</code>

Option 2: Unsafe Conversion

This unsafe method directly converts the underlying data structure:

<code class="go">return *(*ListSociete)(unsafe.Pointer(&res)), nil</code>

This method should be used with caution as it may cause unexpected behavior.

_Playground Example: http://play.golang.org/p/lfk7qBp2Gb

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