Cargo Features

maxminddb has no features set by default.

[dependencies]
maxminddb = { version = "0.23.0", features = ["mmap", "unsafe-str-decode"] }
mmap = memmap2
unsafe-str-decode

Features from optional dependencies

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

memmap2 mmap?

Enables memmap2 ^0.5.0