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### 2757. `std::string{}.insert(3, "ABCDE", 0, 1)` is ambiguous

Section: 21.3.3.7.4 [string.insert] Status: Resolved Submitter: Marshall Clow Opened: 2016-07-30 Last modified: 2020-09-06

Priority: 1

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Discussion:

Before C++17, we had the following signature to `std::basic_string`:

>     basic_string&
>       insert(size_type pos1, const basic_string& str, size_type pos2, size_type n = npos);

Unlike most of the other member functions on `std::basic_string`, there were not corresponding versions that take a `charT*` or `(charT *, size)`.

In p0254r2, we added:

>     basic_string&
>       insert(size_type pos1, basic_string_view<charT, traits> sv, size_type pos2, size_type n = npos);

which made the code above ambiguous. There are two conversions from "`const charT*`", one to `basic_string`, and the other to `basic_string_view`, and they're both equally good (in the view of the compiler).

This ambiguity also occurs with the calls

>     assign(const basic_string& str,             size_type pos, size_type n = npos);
>     assign(basic_string_view<charT, traits> sv, size_type pos, size_type n = npos);

but I will file a separate issue (2758) for that.

A solution is to add even more overloads to `insert`, to make it match all the other member functions of `basic_string`, which come in fours (`string`, `pointer`, `pointer + size`, `string_view`).

[2016-08-03, Chicago, Robert Douglas provides wording]

Previous resolution [SUPERSEDED]:

> This wording is relative to N4606.

> 1. In 21.3.3 [basic.string] modify the synopsis for `basic_string` as follows:

>    >     namespace std {
>    >       template<class charT, class traits = char_traits<charT>,
>    >         class Allocator = allocator<charT>>
>    >       class basic_string {
>    >       public:
>    >         […]
>    >         template<class T>
>    >         basic_string& insert(size_type pos1, basic_string_view<charT, traits>T sv,
>    >                              size_type pos2, size_type n = npos);
>    >         […]
>    >       };
>    >     }

> 2. In 21.3.3.7.4 [string.insert], modify `basic_string_view` overload as follows:

>    >     template<class T>
>    >     basic_string& insert(size_type pos1, basic_string_view<charT, traits>T sv,
>    >                          size_type pos2, size_type n = npos);

>    > > […]

>    > > -?- Remarks: This function shall not participate in overload resolution unless `is_same_v<T, basic_string_view<charT, traits>>` is `true`.

[2016-08-04, Chicago, Robert Douglas comments]

For the sake of simplicity, the previous wording suggestion has been merged into the proposed wording of LWG 2758.

[08-2016, Chicago]

Fri PM: Move to Tentatively Ready (along with 2758).

[2016-09-09 Issues Resolution Telecon]

Since 2758 has been moved back to Open, move this one, too

[2016-10 Telecon]

Ville's wording for 2758 has been implemented in libstdc++ and libc++. Move 2758 to Tentatively Ready and this one to Tentatively Resolved

Proposed resolution:

This issue is resolved by the proposed wording for LWG 2758.