CODEWITHSUNDEEP
go
jdk2588
jdk2588

Reputation: 792

How to override variables from nested packages in go language?

How do I override variables in go from package ?

For example:

file1.go

package A

import "A/B"

var Arg1 = "Hello"

file2.go

package A/B

var Arg1 = "World"

How can I override arg1 in file1.go if arg1 exist in file2.go?

Upvotes: 3

Views: 3736

Answers (4)

hparquet
hparquet

Reputation: 41

You could probably do it using a build flag :

go build -ldflags="-X 'package_path.variable_name=new_value'"

Couple of things to be aware of though :

In order to use ldflags, the value you want to change must exist and be a package level variable of type string. This variable can be either exported or unexported. The value cannot be a const or have its value set by the result of a function call

You'll find all the information needed in this excellent post from DO team

Upvotes: 1

peterSO
peterSO

Reputation: 166714

Are you trying to do something like this, where, for example, a specific location (USA), if present, overrides a general location (World)?

// file A/B.go

package B

var location = "USA"

func Location() string {
    return location
}

// file A.go

package A

import "A/B"

var location = "World"

func Location() string {
    loc := B.Location()
    if len(loc) == 0 {
        loc = location
    }
    return loc
}

// file main.go

package main

import (
    "A"
    "fmt"
)

func main() {
    fmt.Println("Hello,", A.Location())
}

Output:

Hello, USA

If not, please provide a better and specific example of what you are trying to do.

Upvotes: 1

zzzz
zzzz

Reputation: 91321

I'm not sure what you mean by "overriding" in this case. (Also let me assume file1.go is 'package a' and file2.go is 'package b')

If you mean to access Arg1, defined in package "b" inside/from within package "a", then eg.:

// In package "a"
x = Arg1    // references a.Arg1
y = b.Arg1  // references b.Arg1

However, nothing resembling overriding happens here. In package "a" both a's Arg1 and b's Arg1 are accessible as different entities; the later via a mandatory qualifier 'b'.

Upvotes: 3

Volker
Volker

Reputation: 42431

You can't. Packages are self-contained. If package A doesn't export arg1 (lowercase) it is not visible -- and thus not set-able -- for an other package B.

BTW: "package A/B" looks pretty strange to me.

Upvotes: 1

Related Questions