CODEWITHSUNDEEP
go
Benjamin Malley
Benjamin Malley

Reputation: 223

Can I obtain a pointer to a map value in golang?

I'm trying to use Go's flag package to dynamically generate FlagSets and collect the results in a map from flagname -> flag value.

My code looks like this:

import "flag"

fs := flag.NewFlagSet(strings.Join(commands, " "), flag.ExitOnError)
requiredFlags := []string{"flagA", "flagB"}
flags := make(map[string]string)

for _, f := range requiredFlags { 
    flags[f] = *fs.String(f, "", "") 
}

This code compiles, but the map never gets updated after the FlagSet fs is parsed, so the values of "flagA" and "flagB" are both "". So this makes sense to me; flags is of type map[string]string after all, not map[string]*string. Unfortunately, I can't seem to fix this problem using pointers. I've tried every combination of referencing and dereferencing I can think of and I either end up with a nil pointer dereference (runtime error) or invalid indirect (compile time error).

How can I set up the map and FlagSet such that the map values are populated after the FlagSet is parsed?

Upvotes: 0

Views: 5335

Answers (1)

Volker
Volker

Reputation: 42486

What is wrong with

flags := make(map[string]*string)
for _, f := range requiredFlags { 
    flags[f] = fs.String(f, "", "") 
}
...
println(*(flags["flagA"]))

?

Upvotes: 4

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