前言
最近在學 Go，而之前有一些 C 的基礎，因此在學到 Go 的 Array 時，發現它和 C 的 Array 差異性蠻大的，所以特別記錄下來。
Array
Go
1students := [3]string{"student1", "student2", "student3"}
C
1char *students[3] = {"student1", "student2", "student3"}
Go’s arrays are values.
首先，最大的不同點是： Go 的 Array 是一個 Value，也就是 students 這個 Variable 就代表整個 Array 。反之， C 在宣告 Array 後， students 是代表指向 Array 第一個 element 的 pointer，而不是整個 Array。
1// C
2char *students[3] = { "student1", "student2", "student3" };
3char **p;
4p = students; // `students` represents the first element of array.
5printf (*p); // Output: student1
這也意味著， 在 Ｃ 中， Array type 是無法進行 assign.
C - Assignment operator shall have a modifiable lvalue as its left operand. A modifiable lvalue is an lvalue that does not have array type.
1// C
2char* copy[3];
3copy = student; //Error: assignment to expression with array type.
而 Go 的 Array 是一個 Value，所以可以進行 assign.
1var copy [3]string
2copy = students
3fmt.Println(copy) //Output: ["student1", "student2", "student3"]
不過，由於 Go 的 Array 是一個 Value，所以當作為 function 的傳入參數，或著 assign 給其他 Array時，會 copy Array 中的所有 elements，也就是裡面的 element memory address 是完全不一樣的，因此即使在 function 內修改 element 的值，並不會影響到既有的 Array。
1func main() {
2 students := [3]string{"student1", "student2", "student3"}
3 changeName(students) //Output: [student4 student2 student3]
4 fmt.Println(students) // Output: [student1 student2 student3]
5}
6
7func changeName(students [3]string) {
8 students[0] = "student4"
9 fmt.Println(students)
10}
Go’s arrays are values. An array variable denotes the entire array; it is not a pointer to the first array element (as would be the case in C). This means that when you assign or pass around an array value you will make a copy of its contents. (To avoid the copy you could pass a pointer to the array, but then that’s a pointer to an array, not an array.)
There are major differences between the ways arrays work in Go and C. In Go,
最後引用官方 Effective Go 提到的不同點。
- Arrays are values. Assigning one array to another copies all the elements.
- In particular, if you pass an array to a function, it will receive a copy of the array, not a pointer to it.
- The size of an array is part of its type. The types [10]int and [20]int are distinct.