microsoft / microsoft/STL

<format>: `format_to(back_inserter(string), ...)` should reserve space.

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format performance
Dominant language
C++
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Description

Much like the special treatment of string added in #1894, format_to should try to detect that a string is passed and reserve string.size() + _Fmt.size() + _Args._Estimate_required_capacity(). This would make format_to a string just as fast as format

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Research direction

Start by locating the format_to implementation and the string back inserter path in the STL sources. Trace how format currently reserves capacity and how _Fmt and _Args estimate required capacity. Done means format_to with a string reserves the proposed capacity and has tests or measurements showing behavior comparable to format.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
performance
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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