How to check if a map contains a key in Go?

grokus picture grokus · Jan 12, 2010 · Viewed 653.1k times · Source

I know I can iterate over a map m by,

for k, v := range m { ... }

and look for a key but is there a more efficient way of testing a key's existence in a map?

I couldn't find the answer in the language spec.


marketer picture marketer · Jan 12, 2010

One line answer:

if val, ok := dict["foo"]; ok {
    //do something here


if statements in Go can include both a condition and an initialization statement. The example above uses both:

  • initializes two variables - val will receive either the value of "foo" from the map or a "zero value" (in this case the empty string) and ok will receive a bool that will be set to true if "foo" was actually present in the map

  • evaluates ok, which will be true if "foo" was in the map

If "foo" is indeed present in the map, the body of the if statement will be executed and val will be local to that scope.