Cargo Features

d4-framefile has no features set by default.

[dependencies]
d4-framefile = { version = "0.3.9", features = ["mapped_io"] }
mapped_io = memmap

Affects d4-framefile::mapped, randfile::mapping

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features.

memmap mapped_io?