92 lines
1.7 KiB
Plaintext
92 lines
1.7 KiB
Plaintext
---
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title: Classes
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description: Class declarations, constructors, inheritance, virtual dispatch, and the override keyword.
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icon: Shapes
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---
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Mist introduces `class` as syntactic sugar for a Rust struct with a virtual method table (vtable).
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```mist
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pub class Animal
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{
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str& name;
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pub constructor(str& name)
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{
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self.name = name;
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}
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pub void speak(&self)
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{
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println!("...");
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}
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}
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```
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Class fields can have default initializers:
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```mist
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class Player
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{
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i32 health = 100;
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str& name;
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}
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```
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### Inheritance
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```mist
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class Dog : Animal
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{
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pub constructor(str& name)
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{
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super = Super::new(name);
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}
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void speak(&self) override
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{
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println!("Woof!");
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}
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}
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```
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The `override` keyword supports explicit base class targeting (Required if overriding a nested parent):
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```mist
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void speak(&self) override(Animal)
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{
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println!("Woof!");
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}
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```
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### Implementations
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You can implement directly on the class body:
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```mist
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class Circle
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{
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constructor() {}
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impl std::fmt::Display
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{
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Result<(), std::fmt::Error> fmt(&self, Formatter<'_> f)
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{
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write!(f, "●")
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}
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}
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}
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```
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### Under the Hood
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A class `Dog : Animal` generates:
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1. A Rust struct with a `_super: Animal` field (or `_vptr: &'static [*const c_void]` for root classes)
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2. A vtable constant with function pointers for each public method
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3. An `impl` block with `Deref<Target = Animal>` and `DerefMut`
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4. Method trampolines (`__m_<name>`) that are dispatched through the vtable
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5. A `new()` constructor that initializes via `MaybeUninit` and calls the user's `constructor(&mut self)`
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The vtable is unified: parent entries are copied, overridden entries replace parent slots, and new methods are appended.
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