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### 2318. `basic_string`'s wording has confusing relics from the copy-on-write era

Section: 23.4.3 [basic.string] Status: Resolved Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last modified: 2018-11-25

Priority: 4

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Discussion:

23.4.3.5 [string.capacity]/8 specifies `basic_string::resize(n, c)` with:

> Effects: Alters the length of the string designated by `*this` as follows:

> - If `n <= size()`, the function replaces the string designated by `*this` with a string of length `n` whose elements are a copy of the initial elements of the original string designated by `*this`.

> - If `n > size()`, the function replaces the string designated by `*this` with a string of length `n` whose first `size()` elements are a copy of the original string designated by `*this`, and whose remaining elements are all initialized to `c`.

This wording is a relic of the copy-on-write era. In addition to being extremely confusing, it has undesirable implications. Saying "replaces the string designated by `*this` with a string of length `n` whose elements are a copy" suggests that the trimming case can reallocate. Reallocation during trimming should be forbidden, like `vector`.

At least 7 paragraphs are affected: 23.4.3.5 [string.capacity]/8, 23.4.3.7.2 [string.append]/9, 23.4.3.7.3 [string.assign]/3 and /10, 23.4.3.7.4 [string.insert]/11, 23.4.3.7.5 [string.erase]/4, and 23.4.3.7.6 [string.replace]/11 say "replaces the string [designated/controlled] by `*this`". (23.4.3.7.7 [string.copy]/3 is different — it "replaces the string designated by `s`".)

Of the affected paragraphs, `resize()` and `erase()` are the most important to fix because they should forbid reallocation during trimming.

Resolved by the adoption of P1148 in San Diego.

Proposed resolution: