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MathUtils: declare fastATan2's Pi where its lambdas can use it - #15949
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The local constexpr T Pi sits outside the two lambdas that read it. For a builtin T every use is an lvalue-to-rvalue conversion on a constant, so Pi is not odr-used and needs no capture. For a class type the operator call odr-uses it, which a lambda with no capture-default cannot do. Capturing it would not help either, because C, Pi025 and Pi075 are constexpr and a captured variable is not a constant expression. Declaring Pi inside each lambda satisfies both, and costs nothing: it is folded at compile time either way.
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davidrohr
approved these changes
Oct 14, 2026
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The local constexpr T Pi sits outside the two lambdas that read it. For a builtin
T every use is an lvalue-to-rvalue conversion on a constant, so Pi is not
odr-used and needs no capture. For a class type the operator call odr-uses it,
which a lambda with no capture-default cannot do.
Capturing it would not help either, because C, Pi025 and Pi075 are constexpr and
a captured variable is not a constant expression. Declaring Pi inside each lambda
satisfies both, and costs nothing: it is folded at compile time either way.