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Metamethods
Rohan Singh edited this page Jun 24, 2017
·
15 revisions
Metamethods are functions that are called when performing operations on objects. They are used to implement operator overloading but cannot override default behavior.
Metamethods are always called on the x
value of the operation and will pass all relevant values to the handler (x
, y
, z
, w
in the table).
Note: Metamethods should not be called directly. They will not work properly when the object has this
values enabled.
Metamethods can be set for an object by setting special indexes to the function you want it to call.
const endl = {};
const cout = {
__lshift: fun (left, right) {
if (right == endl)
printLn();
else
print(right);
return left;
}
};
cout << "hello " << "world" << endl;
Name | Operation | Called when... |
---|---|---|
__get |
x.y , x[y]
|
attempting to get a value that does not exist in the object |
__set |
x.y = z , x[y] = z
|
attempting to set a value that does not exist in the object, should return the value |
__call |
x(...y) |
attempting to call the object |
__eq |
x == y |
checking if the object is equal to another value, != negates the result of this |
__gt |
x > y |
|
__gte |
x >= y |
|
__lt |
x < y |
|
__lte |
x <= y |
|
__in |
y in x |
note: called on x
|
__add |
x + y |
|
__sub |
x - y |
|
__mul |
x * y |
|
__div |
x / y |
|
__mod |
x % y |
|
__pow |
x ** y |
|
__neg |
-x |
|
__and |
x & y |
|
__or |
x | y |
|
__xor |
x ^ y |
|
__lshift |
x << y |
|
__rshift |
x >> y |
|
__not |
~x |
|
__slice |
x[y:z:w] |
missing values for y , z and w will be undefined
|
__number |
n/a | implicitly converting the object to a number (passes x ) |
__bool |
n/a | implicitly converting the object to a bool (passes x ) |
__string |
n/a | implicitly or explicitly converting the object to a string (passes x ) |
__serialize |
n/a | the object is being serialized, does not need to return a string (passes x ) |
__hash |
n/a | the object is being used as a key in another object |