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Programming-Idioms

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Idiom #51 Check if map contains key

Determine whether the map m contains an entry for the key k

m.hasOwnProperty(k)

This is like "k in m" except it doesn't check up the prototype chain, which is often not what people want.
k in m

This will lookup a property in the object and its entire prototype chain.
_m.has(_k)

Uses an actual Map instance, rather than relying on objects and their keys
M.Contains (K)
New implementation...
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programming-idioms.org 
m.hasOwnProperty(k)
k in m
_m.has(_k)
M.Contains (K)
(contains? m k)
bool key_exists = m.find(k) != m.end();
bool key_exists = m.contains(k);
bool key_exists = m.count(k) != 0;
bool keyExists = m.ContainsKey(key)
if (k in m) { }
m.containsKey(k)
Map.has_key?(m, k)
maps:is_key(K, M).
_, ok := m[k]
Map.member k m
(/=Nothing) (lookup k m)

m.containsKey(k)
m.containsKey(k)
(nth-value 1 (gethash k m))
m[k] ~= nil
if (m[k]) ...
array_key_exists($k, $m)
m.IndexOf(k) >= 0
exists $m->{$k}
m.get(k)
k in m
m.key?(k)
m.has_key?(k)
m.include?(k)

m.contains_key(&k)
m.contains(k)
(assoc k m)
m includesKey: k.
If m.ContainsKey(k) Then...