In Go language, deep copying map or slice requires manual implementation. 1. For maps, you need to traverse the original map and copy the key-value pairs one by one to the new map; if the key or value is a reference type, you also need to recursively copy it. 2. For slices, you can use the built-in copy function to copy elements to the new slice; if it contains nested structures, it needs to be copied layer by layer. 3. Another common method is to use gob or json package serialization and deserialization. It is suitable for complex structures but has low performance, and you need to pay attention to type registration and information loss issues.
In Go language, if you want to actually copy a map or slice so that the new object and the original object do not affect each other, you cannot rely on simple assignment operations. Because by default, Go's assignment is shallow copy, which means that the copied variable and the original variable point to the same memory area. To implement deep copy, it needs to be processed manually.
The following are the deep copy methods of map and slice, which are practical and not difficult to master.
How to copy a map deeply?
In Go, map is a reference type. Directly using = assigns just copy the reference, modifying one of them will affect the other. So you need to iterate through the map yourself and copy the key values one by one.
original := map[string]int{
"a": 1,
"b": 2,
}
copy := make(map[string]int, len(original))
for k, v := range original {
copy[k] = v
}This way you can get an independent copy. Notice:
- If the key or value is a complex structure (such as a nested map, slice, or pointer), you also need to make a recursive deep copy of them.
- If value is a pointer type, the above method can only copy the pointer address and cannot prevent the underlying data from being modified.
How to copy a slice deep?
slice is also a reference type, and simple assignment will share the underlying array. However, you can use the built-in copy() function to copy elements.
original := []int{1, 2, 3}
copy := make([]int, len(original))
copy(copy, original)This code creates a new array and copies all elements, and then the two slices become independent of each other.
But pay attention to the following points:
- If the slice contains reference types (such as
[]*MyStruct,[][]intetc.), you not only have to copy the top-level slice, but also make a deep copy of each child element separately. - For nested structures, it may be necessary to write a helper function to recursively copy.
For example, if it is a two-dimensional slice:
original := [][]int{{1, 2}, {3, 4}}
copy := make([][]int, len(original))
for i := range original {
copy[i] = make([]int, len(original[i]))
copy(copy[i], original[i])
}In this way, each layer is deeply copied to completely isolate.
Is there a more general way?
If you don't want to write these copy logic manually, you can consider using serialization to make deep copy. For example, serialization and deserialization are performed through encoding/gob or json packages. This method is suitable for most structures.
func deepCopy(src, dst interface{}) error {
buf := new(bytes.Buffer)
enc := gob.NewEncoder(buf)
dec := gob.NewDecoder(buf)
if err := enc.Encode(src); err != nil {
return err
}
return dec.Decode(dst)
}Although this method is simple to write, its performance is not as good as manual copying, and is suitable for scenarios with complex structures or insensitive to performance.
Need to note:
- You need to register a custom type before using
gob. - The
jsonmethod will lose some information (such as the difference betweennilslice and empty slice).
Basically that's it. Go does not have a built-in deep copy function, but it is not difficult to implement it yourself as long as you understand the reference mechanism. The key is to choose the appropriate method according to the data structure: simple structures are copied manually the fastest, and complex structures can be guaranteed by serialization.
The above is the detailed content of How to make a deep copy of a map or slice in Go?. For more information, please follow other related articles on the PHP Chinese website!
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