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My program changed its behavior after updating Visual Studio to the latest version (2026).

Simplifying it, I got the following minimal example, which contains a ternary operator with a throw in inactive branch:

constexpr int x = [] { struct { int vs[3]; } a{}; auto && v = (true ? a : throw 0).vs[0]; v = 1; return a.vs[0]; }(); // x = 1 in VS2022 v17.13 // x = 0 in VS2022 v17.14.14 and VS2026 v18.0.0

In Visual Studio 2022 v17.13, x evaluated to 1. But in the latest Visual Studios: both 2022 v17.14.14 and the recently released Visual Studio 2026 v18.0.0, x already evaluates to 0. Online demo.

Which result is correct here if the program is well formed?

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  • Looks like a bug in Visual Studio. You should file a bug with Microsoft. Commented Nov 15 at 22:27
  • Relevant: stackoverflow.com/a/1213076/4706785 Commented Nov 15 at 23:54

1 Answer 1

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Before resolution of CWG 1560 lvalue-to-rvalue conversion would have been applied to a, i.e. you would have ended up binding the reference to a new temporary object. Meaning you get 0 as result.

After resolution via CWG 1550 this is not done anymore and you should get 1 as result.

So this looks like a regression in MSVC.

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