mismatched types *string and string

Question

I am attempting to run a conditional to basically see if the object is empty but I keep getting (similar variations) of this error:

invalid operation: release.Name == "" (mismatched types *string and string)

Here is the code that is dying:

import (
    "github.com/google/go-github/github"
)

func TestLatestTag(user, project string) {

    var client *github.Client
    client = github.NewClient(nil)

    releases, _, err := client.Repositories.ListTags(user, project, nil)
    var release github.RepositoryTag

    if err != nil {
        fmt.Println("Error")
    } else {
        if release.Name == "" {
            fmt.Println("None")
        } else {
            fmt.Println(releases[0])
        }
    }
}

If I change the if statement to *release.Name == "" as the error suggests I get a different error, which I don't really understand:

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x26fd]

goroutine 1 [running]:

I'm sure there is any easy way to do this but I am not very familiar with handling objects/structs

Aruna Herath Aruna Herath · Accepted Answer · 2015-11-22T08:45:58

From the error message it looks like you are trying to compare a string pointer (*string) to an actual string.

release.Name is a *string (a pointer to a string value)
"" is a string (is a string value)

They are two different types. So you can't compare them.

What you probably want to do instead is release.Name == nil

When a pointer that references to nothing (equals to nil) is tried to be dereferenced you get that second error. So in your case *release.Name panics because infact release.Name is nil

mismatched types *string and string

3 Answers