bugprone-fold-init-type

The check flags type mismatches in folds that might result in loss of precision.

The check supports the following functions:

• std::accumulate

• std::reduce

• std::inner_product

These functions fold an input range into an initial value using the type of the latter. By default, std::accumulate and std::reduce use operator+ while std::inner_product uses operator+ and operator*. This can cause loss of precision through:

• Truncation: The following code uses a floating point range and an int initial value, so truncation will happen at every application of operator+ and the result will be 0, which might not be what the user expected.

auto a = {0.5f, 0.5f, 0.5f, 0.5f};
return std::accumulate(std::begin(a), std::end(a), 0);

• Overflow: The following code also returns 0.

auto a = {65536LL * 65536 * 65536};
return std::accumulate(std::begin(a), std::end(a), 0);

The check handles overloads with the following transparent standard functors:

• std::plus

• std::minus

• std::multiplies

• std::divides

• std::bit_and

• std::bit_or

• std::bit_xor