英文:
What the difference between (*T)(nil) and &T{}/new(T)? Golang
问题
这两种表示法之间的微妙区别是什么？(*T)(nil)/new(T)和&T{}。
type Struct struct {
Field int
}
func main() {
test1 := &Struct{}
test2 := new(Struct)
test3 := (*Struct)(nil)
fmt.Printf("%#v, %#v, %#v \n", test1, test2, test3)
//&main.Struct{Field:0}, &main.Struct{Field:0}, (*main.Struct)(nil)
}
似乎这个(*T)(nil)与其他表示法的唯一区别是它返回空指针或无指针，但仍为结构体的所有字段分配内存。
英文:
Could anybody explain what the subtle difference between these two notations: (*T)(nil)/new(T) and &T{}.
type Struct struct {
Field int
}
func main() {
test1 := &Struct{}
test2 := new(Struct)
test3 := (*Struct)(nil)
fmt.Printf("%#v, %#v, %#v \n", test1, test2, test3)
//&main.Struct{Field:0}, &main.Struct{Field:0}, (*main.Struct)(nil)
}
Seems like the only difference of this one (*T)(nil) from other is that it returns nil pointer or no pointer, but still allocates memory for all fields of the Struct.
答案1
得分: 13
两种形式new(T)和&T{}是完全等价的：它们都分配了一个零值的T并返回指向该分配内存的指针。唯一的区别是，&T{}不能用于内置类型如int；你只能使用new(int)。
形式(*T)(nil)并不分配一个T，它只是返回一个空指针nil指向T。你的test3 := (*Struct)(nil)只是对惯用的var test3 *Struct的一个混淆变体。
英文:
The two forms new(T) and &T{} are completely equivalent: Both allocate a zero T and return a pointer to this allocated memory. The only difference is, that &T{} doesn't work for builtin types like int; you can only do new(int).
The form (*T)(nil) does not allocate a T it just returns a nil pointer to T. Your test3 := (*Struct)(nil) is just a obfuscated variant of the idiomatic var test3 *Struct.
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