Function parameter passing in Go is essentially passing values. All parameter passing is a value passed, that is, the function receives a copy of the variable; but it may show a "passing reference" behavior through pointers, slices, maps and other types. 1. The basic data types such as int, string, and bool pass values, and the modification within the function does not affect external variables; 2. The structure and array are also passed values, copy the entire data structure. If you need to modify the original data, you can use a pointer; 3. Although Slice and map also pass values, they contain addresses pointing to the underlying data, so modification within the function will affect the original data; 4. Use pointer to pass parameters to simulate "passing references", and the function modifys the original variables through pointers. In short, Go language always adheres to the value transfer mechanism, and the so-called "passing reference" is just a side effect caused by specific types of characteristics.
Is it possible to pass function parameters in Go to pass values ??or references? Simply put, all parameter passing in Go language is passed values . That is, when you pass a variable to a function, the function receives a copy of the variable, not the original variable itself.
However, although Go is passing values ??by default, you may see behavior similar to "passing references" through pointers, slices, maps, etc. Let’s take a look at several common situations.
Basic data type: typical pass value
Basic types such as int , string , and bool are indeed completely copied when they are passed into functions as parameters.
func modify(n int) {
n = 100
}
a := 5
modify(a)
fmt.Println(a) // Output is still 5 As you can see here, the modification of n inside the function will not affect the external a . Because what is passed in is a copy of the value of a .
Structure and array: also pass values, but may be a bit "heavy"
Structures and arrays are also value-transfer operations when passing parameters. If you pass a large structure or array in, you will copy the data of the entire structure, which may affect performance.
type User struct {
name string
age int
}
func changeUser(u User) {
u.name = "Tom"
}
user := User{name: "Jerry", age: 3}
changeUser(user)
fmt.Println(user.name) // output or JerrySo, if we want the function to modify the original structure, we usually pass a pointer:
func changeUserPtr(u *User) {
u.name = "Tom"
}This looks like a "passing reference", but it is still essentially a pass-through value - it is just a pass-through value.
Slice and Map: It looks like passing a reference, but it is actually passing a value
Many people mistakenly think that slice or map is a "reference type" so they pass references, but in fact they also pass values, but they pass a copy of the structure containing the underlying data address.
For example slice:
func modifySlice(s []int) {
s[0] = 99
}
nums := []int{1, 2, 3}
modifySlice(nums)
fmt.Println(nums) // Output [99 2 3]Although the content of the slice is modified in the function, it is because the underlying array is shared by multiple slices. But this does not change the nature of the Go language parameter passing value.
Similarly, maps are the same:
func addEntry(m map[string]int) {
m["new"] = 42
}
myMap := make(map[string]int)
addEntry(myMap)
fmt.Println(myMap) // Contains new key-value pairsBecause the map variable passed in is a pointer wrapper to the internal structure, the function can modify the original content, but this is still a side effect under the "value pass" mechanism.
Pointer parameter transfer: simulates the method of "passing reference"
If you want the function to actually modify the variable passed in, the most direct way is to use pointers:
func updateValue(v *int) {
*v = 10
}
x := 5
updateValue(&x)
fmt.Println(x) // Output 10In this way, the function gets the address of the variable and can indirectly modify the original variable through a pointer. But please note that even if you pass a pointer, its address value is still copied from the past, which is the so-called "pointer value".
In general, Go always insists that there is only one way to pass parameters: pass values . As for some of the "passing references" behaviors you see, they are actually based on the effects brought by features such as pointers, slices, and maps. Understanding this will help you write clearer, safer, and more efficient code.
Basically that's it.
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