Type Parameters

bitvec uses type parameters to permit precise user control of its behavior and in-memory representation. The Rust generic system permits bitvec to have a more powerful and capable behavior than any other bitstream library yet implemented in any language.

All bitvec types take two type parameters. The first denotes the storage type being used: for everything but BitArray, this is an implementor of the BitStore trait, and denotes the integer component of an underlying slice; for BitArray, it is an implementor of BitViewSized, and is the entire storage block. The second is an implementor of BitOrder, and informs how the structure translates a semantic index into a memory access.

The combination of these two parameters governs how a bitvec type computes its accesses to memory.

The next two chapters describe each trait and their implementors in more detail. You may be able to skip them with this sentence as a good-enough summary:

Use <Lsb0, usize> as the parameters if you are implementing a collection and do not care about memory layout; if you are implementing an I/O protocol specification, the specification document will tell you what ordering and unit size it requires.

Rust syntax requires explicitly choosing type parameters when using generic expressions, such as BitVec::<Store, Order>::new(), and will not substitute in the default parameters when attempting to elide the parameters with BitVec::new(). However, Rust will use the default type parameters in patterns: let bv: BitVec = BitVec::new(); will use the default type parameters in the : BitVec type annotation, which then completes the type of the expression on the right side of the assignment =.