Cargo Features

fn-memo = { version = "1.2.0", default-features = false, features = ["sync", "concurrent_hash_map"] }
default = concurrent_hash_map

The concurrent_hash_map feature is set by default whenever fn-memo is added without default-features = false somewhere in the dependency tree.

sync concurrent_hash_map = once_cell

Affects fn-memo::sync

concurrent_hash_map default = chashmap, sync

Affects sync::chashmap

Features from optional dependencies

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

once_cell sync?

Enables once_cell ^0.2

chashmap concurrent_hash_map