• Pascal

m.IndexOf(k) >= 0

• Ada

M.Contains (K)

• Clojure

(contains? m k)

• C++

bool key_exists = m.contains(k);

• C++

bool key_exists = m.count(k) != 0;

• C++

bool key_exists = m.find(k) != m.end();

• C#

bool keyExists = m.ContainsKey(key)

• D

if (k in m) { }

• Dart

m.containsKey(k)

• Elixir

Map.has_key?(m, k)

• Erlang

maps:is_key(K, M).

• Go

_, ok := m[k]

• Haskell

(/=Nothing) (lookup k m)

• Haskell

Map.member k m

• JS

k in m

• JS

_m.has(_k)

• JS

m.hasOwnProperty(k)

• Java

m.containsKey(k)

• Kotlin

m.containsKey(k)

• Lisp

(nth-value 1 (gethash k m))

• Lua

m[k] ~= nil

• Obj-C

if (m[k]) ...

• PHP

array_key_exists($k, $m)

• Perl

exists $m->{$k}

• Python

m.get(k)

• Python

k in m

• Ruby

m.has_key?(k)

• Ruby

m.key?(k)

• Ruby

m.include?(k)

• Rust

m.contains_key(&k)

• Scala

m.contains(k)

• Scheme

(assoc k m)

• Smalltalk

m includesKey: k.

• VB

If m.ContainsKey(k) Then...