llvm / llvm/llvm-project

P3391R2: `constexpr` `std::format`

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c++26 format libc++ wg21-paper
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LLVM
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Description

**Link:** https://wg21.link/P3391R2

Feature-test macro:
```c++
#define __cpp_lib_constexpr_format 202511L // also in
// updated, see LWG4531
#define __cpp_lib_constexpr_string 202511L // also in
```

Contributor guide

Open the contributing guide

Research direction

Start by reading the linked P3391R2 proposal and the LWG4531 note to understand the requested constexpr std::format behavior. Then locate the existing and implementations and their feature-test macro definitions. Done means the proposal is implemented and the listed macros have the specified values.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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