rust : wip.

dev/lang/rust/hashmap.md

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+# Hashmap.
+
+# Create / Use.
+
+```rust
+use std::collections::HashMap;
+
+// Create.
+let mut scores = HashMap::new();
+
+// Insert.
+scores.insert(String::from("Blue"), 10);
+scores.insert(String::from("Yellow"), 50);
+
+// Get.
+let team_name = String::from("Blue");
+let score     = scores.get(&team_name).copied().unwrap_or(0); // .get() returns Option<&i32> hence the .copied().
+
+// Iterate.
+for (key, value) in &scores {
+  println!("{key}: {value}");
+}
+
+// Update.
+scores.insert(String::from("Blue"), 20);          // Overwrite.
+scores.entry(String::from("Blue")).or_insert(20); // Only if not exists.
+let count = scores.entry(String::from("Blue")).or_insert(0);
+*count += 1; // Add, substract etc.
+```

dev/lang/rust/module.md

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+# Module (access control).
+
+# Create module.
+
+## Separate file.
+
+`src/garden.rs`
+
+## Separate dir.
+
+`src/garden/mod.rs`
+
+## Inline / Access control.
+
+Everything is private by default. Use keyword `pub` to make something public.
+
+```rust
+mod sausage_factory {
+  fn get_secret_sauce() -> String {
+    String::from("Ginger")
+  }
+
+  pub fn make_sausage() {
+    get_secret_sauce();
+    println!("sausage!");
+  }
+}
+
+fn main() {
+  sausage_factory::make_sausage();
+}
+```
+
+# Access module.
+
+Use `use` and `as` keywords.
+
+```rust
+use std::io;
+use std::io as IO;
+use std::io::{self, Write};
+use std::collections::*;
+```
+
+```rust
+mod delicious_snacks {
+  pub use self::fruits::PEAR as fruit;
+  pub use self::veggies::CUCUMBER as veggie;
+
+  mod fruits {
+    pub const PEAR: &'static str = "Pear";
+    pub const APPLE: &'static str = "Apple";
+  }
+
+  mod veggies {
+    pub const CUCUMBER: &'static str = "Cucumber";
+    pub const CARROT: &'static str = "Carrot";
+  }
+}
+
+fn main() {
+  println!(
+    "favorite snacks: {} and {}",
+    delicious_snacks::fruit,
+    delicious_snacks::veggie
+  );
+}
+```