Types that are valid to read using VaList::next_arg.

This trait is implemented for primitive types that have a variable argument application-binary interface (ABI) on the current platform. It is always implemented for:

• c_int, c_long and c_longlong
• c_uint, c_ulong and c_ulonglong
• c_double
• *const T and *mut T

Implementations for e.g. i32 or usize shouldn't be relied upon directly, because they may not be available on all platforms.

Safety

When C passes variable arguments, signed integers smaller than c_int are promoted to c_int, unsigned integers smaller than c_uint are promoted to c_uint, and c_float is promoted to c_double. Implementing this trait for types that are subject to this promotion rule is invalid.

This trait is only implemented for 128-bit integers when the platform defines the __int128 type.