我发现一些网络上的地方说Lua运算符是可重载的,但我似乎找不到任何例子。
有人能提供一个例子吗?比如,重载+运算符使其像..运算符一样用于字符串连接?
编辑1:针对Alexander Gladysh和RBerteig的意见:
如果仅在两个操作数类型相同时才能使用运算符重载,并且更改此行为并不容易,那么以下代码为什么有效呢?(我不是要冒犯,我刚开始学这种语言。)
有人能提供一个例子吗?比如,重载+运算符使其像..运算符一样用于字符串连接?
编辑1:针对Alexander Gladysh和RBerteig的意见:
如果仅在两个操作数类型相同时才能使用运算符重载,并且更改此行为并不容易,那么以下代码为什么有效呢?(我不是要冒犯,我刚开始学这种语言。)
printf = function(fmt, ...)
io.write(string.format(fmt, ...))
end
Set = {}
Set.mt = {} -- metatable for sets
function Set.new (t)
local set = {}
setmetatable(set, Set.mt)
for _, l in ipairs(t) do set[l] = true end
return set
end
function Set.union (a,b)
-- THIS IS THE PART THAT MANAGES OPERATOR OVERLOADING WITH OPERANDS OF DIFFERENT TYPES
-- if user built new set using: new_set = some_set + some_number
if type(a) == "table" and type(b) == "number" then
print("building set...")
local mixedset = Set.new{}
for k in pairs(a) do mixedset[k] = true end
mixedset[b] = true
return mixedset
-- elseif user built new set using: new_set = some_number + some_set
elseif type(b) == "table" and type(a) == "number" then
print("building set...")
local mixedset = Set.new{}
for k in pairs(b) do mixedset[k] = true end
mixedset[a] = true
return mixedset
end
if getmetatable(a) ~= Set.mt or
getmetatable(b) ~= Set.mt then
error("attempt to 'add' a set with a non-set value that is also not a number", 2)
end
local res = Set.new{}
for k in pairs(a) do res[k] = true end
for k in pairs(b) do res[k] = true end
return res
end
function Set.tostring (set)
local s = "{"
local sep = ""
for e in pairs(set) do
s = s .. sep .. e
sep = ", "
end
return s .. "}"
end
function Set.print (s)
print(Set.tostring(s))
end
s1 = Set.new{10, 20, 30, 50}
s2 = Set.new{30, 1}
Set.mt.__add = Set.union
-- now try to make a new set by unioning a set plus a number:
s3 = s1 + 8
Set.print(s3) --> {1, 10, 20, 30, 50}