在Go中设置全局条件变量

I want to parse and set a variable conditionally in Go at the global package level based on the value of of an ENV var, so that I don't have to check for it every time in a utility function (as the variable would be declared once at run time). For example, what I want to accomplish is (Go pseudo-code):

import (
    "fmt"
    "os"
    "strconv"
)

// This works to read the value of MYVAR (=true/false)
var myvar string = os.Getenv("MYVAR")

// Apparently this is too much for Go
var myvarbool, _ = strconv.ParseBool(myvar)

// Utility function to check for value
func mycheck() {
    if myvarbool {
        fmt.Print("MYVAR is true")
    }
}

This is a library package, so doesn't have a main() function to do this kind of setup, but I want to be able to use mycheck() in other functions in the library, and don't want to have to read and parse MYVAR every time mycheck() is called.

I'm not sure what problem you had, your code from the OP is valid, also you can have it in one line like:

var myvarbool, _ = strconv.ParseBool(os.Getenv("MYVAR"))

playground

After actually thinking about this for a couple of minutes, I've realised I can just create a wrapper function to do the work, and call that instead (again, largely pseudo-code without extra checks):

var myenvbool bool = myenv("MYVAR")

func myenv(envvar string) bool {
    myenvvalue := os.Getenv(envvar)
    myenvbool, _ := strconv.ParseBool(myenvvalue)
    return myenvbool
}

func checkenv() {
    if myenvbool {
        fmt.Print("myenvbool is true")
    }
}

One way to accomplish what you're looking to do would be to process the environment variable in an init() function, so something like the following would work:

package main

import (
    "fmt"
    "os"
    "strconv"
)

var (
    myvar string = os.Getenv("MYVAR")
    myvarbool bool
)

func init() {
    myvarbool, _ = strconv.ParseBool(myvar)
}

// Utility function to check for value
func mycheck() {
    if myvarbool {
        fmt.Print("MYVAR is true")
    }
}

Playground