# Extra Clang Tools 21.1.8 documentation

## clang-tidy - bugprone-fold-init-type

# bugprone-fold-init-type

The check flags type mismatches in folds like `std::accumulate` that might result in loss of precision. `std::accumulate` folds an input range into an initial value using the type of the latter, with `operator+` by default. 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);