生成：字符串：无效的操作：没有字段或方法字符串

Question

I'm trying to use the stringer cmd so that I can generate String() methods for some int types. Here is how the code looks like

//go:generate stringer -type=MyIntType
type MyIntType int

const (
    resource MyIntType = iota
)
func myfunc(){
print(resource.String())
}

The error I'm getting on go generate command is invalid operation: resource (constant 0 of type MyIntType) has no field or method String which makes sense because there is no String method yet. How am I supposed to fix this error if stringer cmd is supposed to actually generate the String method? Should I use fmt.Sprintf("%s", resource) all over the code ? it looks a bit ugly to me. At least not as nice as resource.String().

Answer 1

Each file must be parsed and type checked by the types library before the methods are generated. This usually doesn't pose a problem, since the String() method is rarely called directly, and is used by passing a value to something like fmt.Println that always checks first for a Stringer.

You can either not call String() yourself:

file: type.go

//go:generate stringer -type=MyIntType
package painkiller

import "fmt"

type MyIntType int

const (
    resource MyIntType = iota
)

func myfunc() {
    fmt.Println(resource)
}

Or you can put the calls in another file, and pass only the files that stringer needs as arguments. With no arguments, stringer checks the package as a whole, but if you provide only a list of files, they assume that some methods may be defined in files not provided.

file: type.go

//go:generate stringer -type=MyIntType type.go
package foo

type MyIntType int

const (
    resource MyIntType = iota
)

file myfunc.go

package foo

func myfunc() {
    print(resource.String())
}