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---@class Optional<T>
---@field private _value unknown
local Optional = {}
Optional.__index = Optional
---@param value any
function Optional.new(value)
return setmetatable({ _value = value }, Optional)
end
local EMPTY = Optional.new(nil)
---@param value any
function Optional.of_nilable(value)
if value == nil then
return EMPTY
else
return Optional.new(value)
end
end
function Optional.empty()
return EMPTY
end
---@param value any
function Optional.of(value)
return Optional.new(value)
end
---@param mapper_fn fun(value: any): any
function Optional:map(mapper_fn)
if self:is_present() then
return Optional.of_nilable(mapper_fn(self._value))
else
return EMPTY
end
end
function Optional:get()
if not self:is_present() then
error("No value present.", 2)
end
return self._value
end
---@param value any
function Optional:or_else(value)
if self:is_present() then
return self._value
else
return value
end
end
---@param supplier fun(): any
function Optional:or_else_get(supplier)
if self:is_present() then
return self._value
else
return supplier()
end
end
---@param supplier fun(): Optional
---@return Optional
function Optional:or_(supplier)
if self:is_present() then
return self
else
return supplier()
end
end
---@param exception any? The exception to throw if the result is a failure.
function Optional:or_else_throw(exception)
if self:is_present() then
return self._value
else
if exception then
error(exception, 2)
else
error("No value present.", 2)
end
end
end
---@param fn fun(value: any)
function Optional:if_present(fn)
if self:is_present() then
fn(self._value)
end
return self
end
---@param fn fun(value: any)
function Optional:if_not_present(fn)
if not self:is_present() then
fn(self._value)
end
return self
end
function Optional:is_present()
return self._value ~= nil
end
return Optional
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