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### 2777. `basic_string_view::copy` should use `char_traits::copy`

Section: 21.4.3.7 [string.view.ops], 21.3.3.7.7 [string.copy] Status: C++17 Submitter: Billy Robert O'Neal III Opened: 2016-09-27 Last modified: 2017-07-30

Priority: 0

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Discussion:

`basic_string_view::copy` is inconsistent with `basic_string::copy`, in that the former uses `copy_n` and the latter uses `traits::copy`. We should have this handling be consistent.

Moreover, the `basic_string::copy` description is excessively roundabout due to copy-on-write era wording.

[Issues processing Telecon 2016-10-7]

P0; set to Tentatively Ready

Removed "Note to project editor", since the issue there has been fixed in the current draft.

Proposed resolution:

This wording is relative to N4606.

1. Change 21.3.3.7.7 [string.copy] as indicated:

   >     size_type copy(charT* s, size_type n, size_type pos = 0) const;

   -?- Let `rlen` be the smaller of `n` and `size() - pos`.

   -2- Throws: `out_of_range` if `pos > size()`.

   -?- Requires: `[s, s + rlen)` is a valid range.

   -3- Effects: Determines the effective length `rlen` of the string to copy as the smaller of `n` and `size() - pos`. `s` shall designate an array of at least `rlen` elements.Equivalent to: `traits::copy(s, data() + pos, rlen)`. [Note: This does not terminate `s` with a null object. — end note]

   The function then replaces the string designated by `s` with a string of length `rlen` whose elements are a copy of the string controlled by `*this` beginning at position `pos`.

   The function does not append a null object to the string designated by `s`.

   -4- Returns: `rlen`.

2. Change 21.4.3.7 [string.view.ops] as indicated:

   >     size_type copy(charT* s, size_type n, size_type pos = 0) const;

   -1- Let `rlen` be the smaller of `n` and `size() - pos`.

   -2- Throws: `out_of_range` if `pos > size()`.

   -3- Requires: `[s, s + rlen)` is a valid range.

   -4- Effects: Equivalent to: `copy_n(begin() + pos, rlen, s)``traits::copy(s, data() + pos, rlen)`

   -5- Returns: `rlen`.

   -6- Complexity: 𝒪(`rlen`).