cannot convert value of type 'String!' to expected argument type 'inout String'

var area_big:String!
var area_small:String!


var types = ""
var firstIn = true

provinces.forEach { (province) in
let count = province.children.count
for i in 0..<count{
if i == 0 && province.children[i].checked {
if area_big == nil {
area_big = province.children[i].attributes["name"]
}else{
area_big += "#" + province.children[i].attributes["name"]!
}

}
}
}

如果是按照上面那样写 ，会报如题错误。改为如下就可以了

var area_big:String! var area_small:String! var types = "" var firstIn = true provinces.forEach { (province) in let count = province.children.count for i in 0..<count{ if i == 0 && province.children[i].checked { if area_big == nil { area_big = province.children[i].attributes["name"] }else{ area_big = area_big + "#" + province.children[i].attributes["name"]! } } } }