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Diffstat (limited to 'vendor/once_cell/examples/lazy_static.rs')
-rw-r--r-- | vendor/once_cell/examples/lazy_static.rs | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/vendor/once_cell/examples/lazy_static.rs b/vendor/once_cell/examples/lazy_static.rs new file mode 100644 index 000000000..f0505609b --- /dev/null +++ b/vendor/once_cell/examples/lazy_static.rs @@ -0,0 +1,36 @@ +extern crate once_cell; + +use once_cell::sync::{Lazy, OnceCell}; +use std::collections::HashMap; + +static HASHMAP: Lazy<HashMap<u32, &'static str>> = Lazy::new(|| { + let mut m = HashMap::new(); + m.insert(0, "foo"); + m.insert(1, "bar"); + m.insert(2, "baz"); + m +}); + +// Same, but completely without macros +fn hashmap() -> &'static HashMap<u32, &'static str> { + static INSTANCE: OnceCell<HashMap<u32, &'static str>> = OnceCell::new(); + INSTANCE.get_or_init(|| { + let mut m = HashMap::new(); + m.insert(0, "foo"); + m.insert(1, "bar"); + m.insert(2, "baz"); + m + }) +} + +fn main() { + // First access to `HASHMAP` initializes it + println!("The entry for `0` is \"{}\".", HASHMAP.get(&0).unwrap()); + + // Any further access to `HASHMAP` just returns the computed value + println!("The entry for `1` is \"{}\".", HASHMAP.get(&1).unwrap()); + + // The same works for function-style: + assert_eq!(hashmap().get(&0), Some(&"foo")); + assert_eq!(hashmap().get(&0), Some(&"bar")); +} |