How to remove the last character of a string in Golang?

No builtin way. But it's trivial to do manually.

s := "mystring+"
sz := len(s)

if sz > 0 && s[sz-1] == '+' {
    s = s[:sz-1]
}

Based on the comment of @KarthikGR the following example was added:

https://play.golang.org/p/ekDeT02ZXoq

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Println(strings.TrimSuffix("Foo++", "+"))
}

returns:

Foo+

Here are several ways to remove trailing plus sign(s).

package main

import (
    "fmt"
    "strings"
)

func TrimSuffix(s, suffix string) string {
    if strings.HasSuffix(s, suffix) {
        s = s[:len(s)-len(suffix)]
    }
    return s
}

func main() {
    s := "a string ++"
    fmt.Println("s: ", s)

    // Trim one trailing '+'.
    s1 := s
    if last := len(s1) - 1; last >= 0 && s1[last] == '+' {
        s1 = s1[:last]
    }
    fmt.Println("s1:", s1)

    // Trim all trailing '+'.
    s2 := s
    s2 = strings.TrimRight(s2, "+")
    fmt.Println("s2:", s2)

    // Trim suffix "+".
    s3 := s
    s3 = TrimSuffix(s3, "+")
    fmt.Println("s3:", s3)
}

Output:

s:  a string ++
s1: a string +
s2: a string 
s3: a string +