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37 lines
1.0 KiB
37 lines
1.0 KiB
4 months ago
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extern crate once_cell;
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use once_cell::sync::{Lazy, OnceCell};
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use std::collections::HashMap;
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static HASHMAP: Lazy<HashMap<u32, &'static str>> = Lazy::new(|| {
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let mut m = HashMap::new();
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m.insert(0, "foo");
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m.insert(1, "bar");
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m.insert(2, "baz");
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m
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});
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// Same, but completely without macros
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fn hashmap() -> &'static HashMap<u32, &'static str> {
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static INSTANCE: OnceCell<HashMap<u32, &'static str>> = OnceCell::new();
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INSTANCE.get_or_init(|| {
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let mut m = HashMap::new();
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m.insert(0, "foo");
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m.insert(1, "bar");
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m.insert(2, "baz");
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m
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})
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}
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fn main() {
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// First access to `HASHMAP` initializes it
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println!("The entry for `0` is \"{}\".", HASHMAP.get(&0).unwrap());
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// Any further access to `HASHMAP` just returns the computed value
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println!("The entry for `1` is \"{}\".", HASHMAP.get(&1).unwrap());
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// The same works for function-style:
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assert_eq!(hashmap().get(&0), Some(&"foo"));
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assert_eq!(hashmap().get(&0), Some(&"bar"));
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}
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