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< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
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< h2 id = "125-通过reflectvalue修改值" > < a class = "header" href = "#125-通过reflectvalue修改值" > 12.5. 通过reflect.Value修改值< / a > < / h2 >
< p > 到目前为止，反射还只是程序中变量的另一种读取方式。然而，在本节中我们将重点讨论如何通过反射机制来修改变量。< / p >
< p > 回想一下， ， < / p >
< p > 对于reflect.Values也有类似的区别。有一些reflect.Values是可取地址的； ： < / p >
< pre > < code class = "language-Go" > x := 2 // value type variable?
a := reflect.ValueOf(2) // 2 int no
b := reflect.ValueOf(x) // 2 int no
c := reflect.ValueOf(& x) // & x *int no
d := c.Elem() // 2 int yes (x)
< / code > < / pre >
< p > 其中a对应的变量不可取地址。因为a中的值仅仅是整数2的拷贝副本。b中的值也同样不可取地址。c中的值还是不可取地址， < code > & x< / code > 的拷贝。实际上， ， ， ， & x).Elem()， < / p >
< p > 我们可以通过调用reflect.Value的CanAddr方法来判断其是否可以被取地址： < / p >
< pre > < code class = "language-Go" > fmt.Println(a.CanAddr()) // " false"
fmt.Println(b.CanAddr()) // " false"
fmt.Println(c.CanAddr()) // " false"
fmt.Println(d.CanAddr()) // " true"
< / code > < / pre >
< p > 每当我们通过指针间接地获取的reflect.Value都是可取地址的， ， ， ， ， ， ， < / p >
< p > 要从变量对应的可取地址的reflect.Value来访问变量需要三个步骤。第一步是调用Addr()方法， ， ， ， ， ， < / p >
< pre > < code class = "language-Go" > x := 2
d := reflect.ValueOf(& x).Elem() // d refers to the variable x
px := d.Addr().Interface().(*int) // px := & x
*px = 3 // x = 3
fmt.Println(x) // " 3"
< / code > < / pre >
< p > 或者， ， ： < / p >
< pre > < code class = "language-Go" > d.Set(reflect.ValueOf(4))
fmt.Println(x) // " 4"
< / code > < / pre >
< p > Set方法将在运行时执行和编译时进行类似的可赋值性约束的检查。以上代码， ， ， ， ： < / p >
< pre > < code class = "language-Go" > d.Set(reflect.ValueOf(int64(5))) // panic: int64 is not assignable to int
< / code > < / pre >
< p > 同样， ： < / p >
< pre > < code class = "language-Go" > x := 2
b := reflect.ValueOf(x)
b.Set(reflect.ValueOf(3)) // panic: Set using unaddressable value
< / code > < / pre >
< p > 这里有很多用于基本数据类型的Set方法： < / p >
< pre > < code class = "language-Go" > d := reflect.ValueOf(& x).Elem()
d.SetInt(3)
fmt.Println(x) // " 3"
< / code > < / pre >
< p > 从某种程度上说， ， ， ， ： ， < / p >
< pre > < code class = "language-Go" > x := 1
rx := reflect.ValueOf(& x).Elem()
rx.SetInt(2) // OK, x = 2
rx.Set(reflect.ValueOf(3)) // OK, x = 3
rx.SetString(" hello" ) // panic: string is not assignable to int
rx.Set(reflect.ValueOf(" hello" )) // panic: string is not assignable to int
var y interface{}
ry := reflect.ValueOf(& y).Elem()
ry.SetInt(2) // panic: SetInt called on interface Value
ry.Set(reflect.ValueOf(3)) // OK, y = int(3)
ry.SetString(" hello" ) // panic: SetString called on interface Value
ry.Set(reflect.ValueOf(" hello" )) // OK, y = " hello"
< / code > < / pre >
< p > 当我们用Display显示os.Stdout结构时， ， ， ： < / p >
< pre > < code class = "language-Go" > stdout := reflect.ValueOf(os.Stdout).Elem() // *os.Stdout, an os.File var
fmt.Println(stdout.Type()) // " os.File"
fd := stdout.FieldByName(" fd" )
fmt.Println(fd.Int()) // " 1"
fd.SetInt(2) // panic: unexported field
< / code > < / pre >
< p > 一个可取地址的reflect.Value会记录一个结构体成员是否是未导出成员， ， ： < / p >
< pre > < code class = "language-Go" > fmt.Println(fd.CanAddr(), fd.CanSet()) // " true false"
< / code > < / pre >
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