Cargo Features

[dependencies]
id-pool = { version = "0.2.2", default-features = false, features = ["usize", "u16", "serde"] }
default = usize

The usize feature is set by default whenever id-pool is added without default-features = false somewhere in the dependency tree.

usize default
u64 u32 u16

Features from optional dependencies

serde implicit feature

Enables serde

serde:

A generic serialization/deserialization framework