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### 2372. Assignment from int to `std::string`

Section: 21.3.3 [basic.string] Status: NAD Submitter: Andrzej Krzemieński Opened: 2014-03-13 Last modified: 2018-06-23

Priority: 4

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Discussion:

The following code works in C++:

>     int i = 300;
>     std::string threeHundred;
>     threeHundred = i;

"Works" == "Compiles and doesn't have an undefined behavior". But it may not be obvious and in fact misleading what it does. This assignment converts an `int` to `char` and then uses `string`'s assignment from `char`. While the assignment from `char` can be considered a feature, being able to assign from an int looks like a safety gap. Someone may believe C++ works like "dynamically typed" languages and expect a lexical conversion to take place.

Ideally the assignment from `char` could be deprecated and later removed, but as a less intrusive alternative one could consider adding a SFINAEd deleted function template:

>     template <typename IntT> // enable if is_integral<IntT>::value
>     basic_string& operator=(IntT) = delete;

[Lenexa 2015-06-06: Move to LEWG]

RS: `std::string x('0' + n);` broken by this.

MC: This is an extension, move to LEWG.

Move to LEWG, consensus.

Previous resolution [SUPERSEDED]:

> This wording is relative to N3936.

> 1. To 21.3.3 [basic.string], class template `basic_string` synopsis, add as indicated:

>    >     basic_string& operator=(const basic_string& str);
>    >     basic_string& operator=(basic_string&& str) noexcept;
>    >     basic_string& operator=(const charT* s);
>    >     basic_string& operator=(charT c);
>    >     template <class IntT> basic_string& operator=(IntT i) = delete;
>    >     basic_string& operator=(initializer_list<charT>);

> 2. Add after 21.3.3.3 [string.cons] p26 as indicated:

>    >     basic_string& operator=(charT c);

>    > > -26- Returns: `*this = basic_string(1,c)`.

>    >     template <class IntT> basic_string& operator=(IntT i) = delete;

>    > > -?- Remarks: This signature shall not participate in overload resolution unless `is_integral<T>::value` is `true`.

[LEWG: 2016-03, Jacksonville]

`is_integral<T>::value` → `is_arithmetic<tmpl-arg>::value`

This needs a paper; close the issue

We don't think the breakage is acceptable.

Guidance to author: Look for a way to encourage a warning; discomfort with calling that "deprecation".

Consider `+=` and `push_back`.

Proposed resolution:

This should be addressed by a paper addressed to LEWG.