CODEWITHSUNDEEP
lualua-table
Alistair -L.
Alistair -L.

Reputation: 13

Compare values of different type in Lua 5.2

I want to overload the == (equality) operator for <number> == <table> and <table> == <number> expressions.

However, it seems to me that Lua only uses the __eq metamethod when the two sides of the equation are of the same type.

For instance, the following snippet does not work as I expected

x = {1,2}
setmetatable (x, {__eq = function (x,y) print "!" return x[y] ~= nil end})
print (x == 1)

but this one does:

x = {1,2}
setmetatable (x, {__eq = function (x,y) print "!" return x[y] ~= nil end})
print (x == {1})

Is it possible to implement == for <number> == <table> and <table> == <number> expressions?

I'm running the latest version (5.2.2).

Upvotes: 1

Views: 283

Answers (2)

Yu Hao
Yu Hao

Reputation: 122383

It's not possible.

If two objects have different basic types, the equality operation results in false, without even calling the metamethod.

Upvotes: 2

lhf
lhf

Reputation: 72312

It is not possible to override equality for values of different types.

Upvotes: 1

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