golang prohibits pointer assignment

In the Golang language, pointers are a very important data type and are widely used in various scenarios. However, Golang prohibits pointer assignment, which is often ignored by people. This article will briefly introduce the reason and implementation mechanism of Golang prohibiting pointer assignment, and explore the design philosophy behind this feature.

1. Why is pointer assignment prohibited?

Since the garbage collection mechanism in Golang uses a reachability analysis algorithm, it is impossible to know whether a variable is referenced by a pointer at runtime. If one pointer is assigned to another pointer, it will be impossible to determine which pointer actually corresponds to the variable that is not used, thus affecting the GC's judgment and recycling effect.

For example:

package main

type person struct {
    name string
}

func main() {
    p1 := &person{"Jack"}
    p2 := &person{"Peter"}
 
    p2 = p1 
}

In the above example, we created two pointers p1 and p2, which point to structures of type person respectively. But when we try to execute p2 = p1, the compiler will prompt: Cannot assign to p2. Because Golang prohibits direct assignment of pointers. If we have to modify the object pointed to by p2 through a pointer, we can use pointer dereference to operate, as shown below:

*p2 = *p1

The benefit of this is not only to make the code safer, but also to improve GC efficiency.

2. Implementation mechanism

So how is the feature of prohibiting pointer assignment in Golang implemented? In fact, it is not complicated. Golang will maintain a special pointer type Value internally to represent variables of pointer type. If a variable is a pointer type, the CanSet property of its corresponding Value is false, so its value cannot be modified through the Value.Set method. This achieves the effect of prohibiting pointer assignment.

3. Design philosophy

From the perspective of design philosophy, Golang’s prohibition of pointer assignment is a manifestation of “Protective Design”. The design philosophy in Golang advocates focusing on compile-time checking to avoid errors at runtime. Prohibiting pointer assignment is the embodiment of this idea. It can help us eliminate some common errors when writing code, thereby improving the reliability and robustness of the program.

In addition, Golang's design also emphasizes simplicity and readability. The prohibition of pointer assignment is also to reduce the complexity and difficulty of the code. The use of pointers often increases the complexity and difficulty of programs, and prohibiting pointer assignment allows developers to focus more on solving practical problems, thereby improving development efficiency.

In short, Golang’s prohibition of pointer assignment may seem like a small restriction, but it reflects Golang’s design philosophy and programming ideas. It can not only improve the reliability and robustness of the program, but also reduce the complexity and difficulty of the code, providing developers with a more concise, efficient, and readable development experience.

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