c++ 编写类似于标准库中find算法的模板，非引用形参和引用形参的区别是什么

#include <iostream>
#include <string>
#include <vector>
using namespace std;
template<typename Init,typename T> Init find(Init begin,Init end,const T& val){
    while(begin!=end){
        if(val==(*begin)){
            return begin;
        }
        ++begin;
    }
    return end;
}
//为什么前2个参数改成引用就不行了
template<typename Init,typename T> Init find_(Init &begin,Init &end,const T& val){
    while(begin!=end){
        if(val==(*begin)){
            return begin;
        }
        ++begin;
    }
    return end;
}

int main(){
    int arr[5] = {1,2,3,45,5};
    string sarr[5] = {"b","c ","dd","ee","ff"};
    vector<int> ivec(arr,arr+5);
    vector<string> svec(sarr,sarr+5);
    vector<int>::iterator it;
    vector<string>::iterator sit;
    if((it=find(ivec.begin(),ivec.end(),3))!=ivec.end()){
        cout << *it << "is in the vector" << endl;
    }else{
        cout << "not found!" << endl;
    }
    if((sit = fd_(svec.begin(),svec.end(),string("b")))!=svec.end()){
        cout << "find" << endl;
    }
    else{
        cout << "not find";
    }
}

把find函数的前两个形参改成引用，会产生编译错误，为什么
error: invalid initialization of non-const reference of type ‘__gnu_cxx::__normal_iterator, std::vector >&’ from an rvalue of type ‘std::vector::iterator {aka __gnu_cxx::__normal_iterator, std::vector >}’

 if((it=find_(ivec.begin(),ivec.end(),3))!=ivec.end()){
                                       ^

error: in passing argument 1 of ‘Init find_(Init&, Init&, const T&) [with Init = __gnu_cxx::__normal_iterator >; T = int]’
template Init find_(Init &begin,Init &end,const T& val){