The AbstractArray interface in Base Julia does not always enforce static guarantees. For example, if the size of an array is known at compile time, many of the indexing schemes are not specialized to make use of that size to build fully optimized code. In most cases a user should rely on the compiler to deduce the static properties and perform the optimization. However, some brave souls believe they can beat the compiler, and this library is for them.

Functions like known_length return values using Static.jl which encode all of the information at the type level, which in turn forces the computation to occur at compile time.

No, not necessarily. StaticArrays.jl is one library about array types which have static compile time information. However, there are many other array types with static compile time information. The purpose of this library is to be able to write code generic to all of those libraries which also keep this property of enforcing the computation is at compile time by using the type space.

Because this library enforces things be done at compile time by encoding everything into types, using it will increase your compile times. You have been warned, now proceed (with caution).