Wait is he really trying to say, "Setting a VALUE to nil removes the entry from the dictionary!"? If so, that sounds terrible.
I can imagine barking up the wrong tree wondering why my map is missing fields when the real problem is an object I passed into it is unexpectedly nil.
//Let's define some object
var obj = {a: true, b: true, c: true, d: true, hasOwnProperty: true}
//Now let's make them falsy in different ways
obj.a = undefined; //set to undefined
obj.b = null; //set to null
obj.c = false; //set to false
delete obj.d; //delete key
delete obj.hasOwnProperty //delete key, but present in prototype
console.log(obj.a) //--> undefined
console.log(obj.b) //--> null
console.log(obj.c) //--> false
console.log(obj.d) //--> undefined
console.log(obj.hasOwnProperty) //--> [Function]
console.log('a' in obj) //--> true
console.log('b' in obj) //--> true
console.log('c' in obj) //--> true
console.log('d' in obj) //--> false
console.log('hasOwnProperty' in obj) //--> true
console.log(obj.a == null) //--> true
console.log(obj.b == null) //--> true
console.log(obj.c == null) //--> false
console.log(obj.d == null) //--> true
console.log(obj.hasOwnProperty == null) //--> false
for(var key in obj) {
console.log(key) //--> prints a, b, c
}
local tab = {a = true, b = true, c = true}
-- by default there are none, but we can defined a fallback metatable similar to a prototype method like js's obj.prototype.hasOwnProperty
setmetatable(tab, {__index={c='meta c', d='meta d'}})
-- if it is important that a key is explicitly set to false, do so, otherwise simply remove it
tab.a = false --set to false
tab.b = nil --set to nil
tab.c = nil --set to nil, present in fallback table
tab.d = false --set to false, present in fallback table
print(tab.a) --false
print(tab.b) --nil
print(tab.c) --meta c
print(tab.d) --false
This is especially important in Lua, because any value can be a key, you would have to be sure to delete the key otherwise it could not be garbage collected. local tab1 = {1,2,3,4,5} local tab2 = {} tab2[tab1] = true for k,v in pairs(tab2) do tab[k] = nil end
If this worked like JavaScript, then tab2[tab1] would return nil, but tab1 could not be garbage collected until tab2 is. Because JavaScript objects can only have strings for keys, this is less of an issue.