英文:
Go: Property of an interface is undefined despite existing in the documentation
问题
我正在编写一个遍历抽象语法树（AST）的程序。当我执行以下代码片段时：
val := reflect.Indirect(reflect.ValueOf(currStatement))
for i := 0; i < val.NumField(); i++ {
varName := val.Type().Field(i).Name
varType := val.Type().Field(i).Type
varValue := val.Field(i).Interface()
if (varName == "Body") {
fmt.Printf("%v %v %v\n", varName,varType,varValue)
}
}
fmt.Println()
我得到以下输出：
Body *ast.BlockStmt &{2795 [0xc0001044c0] 2867}
这表明val.Field(i).Interface()的类型是*ast.BlockStmt。然而，根据这里的文档（https://pkg.go.dev/go/ast#BlockStmt）：
可以明确看到BlockStmt具有属性List。然而，当我在for循环中运行以下代码行以提取属性List的值（最终我将遍历它）：
fmt.Printf("%v %v %v\n", varName,varType,varValue.List)
我得到以下错误：
varValue.List undefined (type interface {} is interface with no methods)
英文:
I am writing a program that iterates through an AST (abstract syntax tree). When I execute the following piece of code:
val := reflect.Indirect(reflect.ValueOf(currStatement))
for i := 0; i < val.NumField(); i++ {
varName := val.Type().Field(i).Name
varType := val.Type().Field(i).Type
varValue := val.Field(i).Interface()
if (varName == "Body") {
fmt.Printf("%v %v %v\n", varName,varType,varValue)
}
}
fmt.Println()
I get the following output:
Body *ast.BlockStmt &{2795 [0xc0001044c0] 2867}
Which indicates that val.Field(i).Interface() is the type *ast.BlockStmt. However, according to the documentation here (https://pkg.go.dev/go/ast#BlockStmt):
It is clear that BlockStmt has the property List. However, when I run the following line of code in the for loop to extract the value of the property List (which I will eventually iterate through):
fmt.Printf("%v %v %v\n", varName,varType,varValue.List)
I get the following error:
varValue.List undefined (type interface {} is interface with no methods)
答案1
得分: 1
varValue 是类型为 interface{} 的变量，指向一个 BlockStmt 实例。你需要使用类型断言来从中获取 BlockStmt：
blk := varValue.(*ast.BlockStmt)
然后你可以访问 blk.List。
英文:
varValue is of type interface{} that points to a BlockStmt instance. You have to use type-assertion to get the BlockStmt from it:
blk:=varValue.(*ast.BlockStmt)
Then you can access blk.List.
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