Printing a reflect.Value

[sb...@google.com]

Hello group,

https://golang.org/pkg/fmt/ says:

1. If the operand is a reflect.Value, the operand is replaced by the concrete value that it holds, and printing continues with the next rule. 

5. If an operand implements method String() string, that method will be invoked to convert the object to a string, which will then be formatted as required by the verb (if any). 

So, in the following program (https://play.golang.org/p/V4H-vkjoE5):

package main

import (
 "fmt"
 "reflect"
)

type SpecialInt int

func (i SpecialInt) String() string { return fmt.Sprintf("SpecialInt(%d)", int(i)) }

func main() {
 v := reflect.ValueOf(SpecialInt(73))
 fmt.Printf("%+v\n", v)
 fmt.Printf("%+v\n", v.Interface())
}

I expect the first fmt.Printf call to substitute the concrete value of v, which is SpecialInt(73), invoke the String() method on it, and print "SpecialInt(73)". However, it just prints "73". On the contrary, the second fmt.Printf call (correctly) prints "SpecialInt(73)".

Is there anything I'm missing here, or maybe something wrong with the Go documentation or implementation?

Thanks.

[Matt Harden]

This definitely seems inconsistent with the documentation, unless you allow the phrase "concrete value" to mean two different things depending on which part of the doc you're reading. Unfortunately that term is not defined in the godoc or the language specification.

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[Rob Pike]

Please file an issue.

[Matt Harden]

https://github.com/golang/go/issues/16015