Merge pull request #14 from mist-go/docs-allman-fixes
Fix Allman brace style and field terminator consistency across docs
This commit is contained in:
@@ -7,8 +7,9 @@ icon: Shapes
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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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str& name,
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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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@@ -25,19 +26,21 @@ pub class Animal {
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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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i32 health = 100,
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str& name,
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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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class Dog : Animal
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{
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pub constructor(str& name)
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{
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super(name);
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super = Super::new(name);
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}
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void speak(&self) override
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@@ -56,6 +59,25 @@ void speak(&self) override(Animal)
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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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@@ -67,3 +89,102 @@ A class `Dog : Animal` generates:
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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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### Safety
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Classes use `MaybeUninit::zeroed().assume_init()` inside the generated `new()` function — an inherently unsafe operation. This raises a natural question: **Are class constructors unsafe?**
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The answer is **no**. The compiler statically verifies that every field is initialized before the constructor returns, eliminating the undefined behavior that raw `MaybeUninit` would normally carry.
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#### Static Field Initialization Verification
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When a class has a constructor, the semantic checker (`check_class_semantics`) collects every declared field and walks the constructor body to prove each one is written to:
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1. **Direct assignment tracking** — Expressions like `self.field = value` are recognized as mutations of `field`. The analyzer checks for `=` and `->` operators whose left-hand side is a `self.field` path.
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2. **`&mut self.field` tracking** — Taking a mutable reference to a field (`&mut self.field`) also counts as initializing it, since the reference can only be taken if the field is being set up.
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3. **Transitive method calls** — If the constructor calls `self.helper()`, the analyzer follows into `helper`'s body and tracks which fields *it* initializes. This transitively propagates through nested calls:
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```mist
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class Player
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{
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str& name;
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i32 health;
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pub constructor(str& name)
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{
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self.name = name;
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self.setup_health();
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}
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void setup_health(&mut self)
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{
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self.health = 100; // Counts toward constructor's verification
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}
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}
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```
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4. **Branch intersection** — For `if`/`else`, `match`, and loops, fields must be initialized in **all** branches. If one branch initializes `x` but another does not, `x` is considered uninitialized. This ensures soundness regardless of the runtime path:
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```mist
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pub constructor(bool flag)
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{
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if flag {
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self.health = 100;
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} else {
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self.health = 0;
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}
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// Both branches init health ✓
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}
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```
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5. **Super initialization** — When a class inherits, the `_super` field is added to the required-field list. Any assignment to `super` counts:
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```mist
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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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```
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If any field is uninitialized after the full analysis, a compile-time error is reported with the field's exact source location:
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```
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class field `Player.health` is uninitialized
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```
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#### Override Validation at Compile Time
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When a method uses the `override` keyword, the codegen emits a hidden test function that verifies the Deref chain at compile time:
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```rust
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#[allow(invalid_value)]
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fn __test_vt() {
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let this: &Self = &unsafe { std::mem::MaybeUninit::<Self>::zeroed().assume_init() };
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let _: &Target = this; // Forces compiler to check Deref<Target = Target>
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}
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```
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This ensures `&Self` can always deref into the base class type. If the inheritance hierarchy is invalid, the Rust compiler rejects it.
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#### VTable Safety
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The `_vptr` (vtable pointer) is set *twice* during construction:
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1. **Before** the constructor body runs — enabling virtual dispatch inside the constructor itself
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2. **After** the constructor body — in case a base-class constructor ran and overwrote the pointer
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This ensures that virtual method calls work correctly even during object construction, without exposing uninitialized memory through the vtable.
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#### Summary
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| Risk | Mitigation |
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|------|-----------|
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| Uninitialized fields via `MaybeUninit` | Static field-initialization verification rejects incomplete constructors |
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| UB from reading uninitialized fields | Intersection analysis ensures all branches init the same fields |
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| Invalid override signatures | Compile-time Deref test validates the inheritance chain |
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| Vtable corruption during construction | `_vptr` is set before and after the constructor body |
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| Unsafe code in generated constructors | `#[allow(invalid_value)]` is scoped to the generated `new()` only |
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The `MaybeUninit` pattern is an implementation detail of the generated code — the Mist compiler proves soundness at the language level, so the user's constructor body is safe Mist code with no manual `unsafe` annotations required.
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@@ -7,17 +7,20 @@ icon: ArrowLeftRight
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### If/Else
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```mist
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if condition {
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if condition
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{
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// body
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} else if other_condition {
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}
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else if other_condition
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{
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// body
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} else {
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}
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else
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{
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// body
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}
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```
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Conditions must be parenthesized: `if (expr) { }` or `if expr_no_struct { }` (struct literals require parentheses).
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Used as an expression:
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```mist
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@@ -27,7 +30,8 @@ let x = if true { 1 } else { 2 };
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### While
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```mist
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while condition {
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while condition
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{
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// body
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}
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```
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@@ -35,11 +39,13 @@ while condition {
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### For
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```mist
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for pattern in iterator {
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for pattern in iterator
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{
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// body
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}
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for i in 0 .. 10 {
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for i in 0 .. 10
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{
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// body
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}
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```
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@@ -47,7 +53,8 @@ for i in 0 .. 10 {
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### C-Style For
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```mist
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for (let mut i = 0; i < 10; i++) {
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for (let mut i = 0; i < 10; i++)
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{
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// body
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}
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```
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@@ -55,7 +62,8 @@ for (let mut i = 0; i < 10; i++) {
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### Loop
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```mist
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loop {
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loop
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{
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// infinite loop
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}
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```
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@@ -42,13 +42,9 @@ unsafe i32 dangerous()
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}
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```
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Function syntax: `[pub] [void | <type>] <name>[<generics>](<params>) [override] { <body> }`
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Functions use **Allman brace style** (opening brace on the next line).
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### Self Parameter
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Methods can take `self`, `mut self`, `&self`, `&mut self` additionally with lifetimes:
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Methods can take `self`, `mut self`, `&self`, `&mut self`, and `&'a self` / `&'a mut self` with lifetimes:
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```mist
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pub void set_value(&mut self, i32 v)
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@@ -12,15 +12,17 @@ T id<T>(T x)
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}
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// Generic struct
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struct Pair<A, B> {
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struct Pair<A, B>
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{
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A first,
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B second,
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}
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// Generic enum
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enum Result<T, E> {
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Ok(T),
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Err(E),
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enum Result<T, E>
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{
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Ok(T);
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Err(E);
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}
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// Generic with trait bounds
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@@ -25,11 +25,11 @@ match value {
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// Named tuple patterns (newtype)
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let MyType(value) = my_var;
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// Wildcard / etc
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// Wildcard / rest
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let _ = get_side_effect();
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match x {
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1 => ...,
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.. => ..., // rest / etc
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1 => expr,
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.. => expr, // rest / etc
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}
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// Mutable binding in pattern
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@@ -7,12 +7,14 @@ icon: Box
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### Structs
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```mist
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pub struct Point {
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pub struct Point
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{
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i32 x,
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i32 y,
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}
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pub struct Generic<T> {
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pub struct Generic<T>
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{
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T value,
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}
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```
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@@ -20,7 +22,8 @@ pub struct Generic<T> {
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Fields can be public or private:
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```mist
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struct User {
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struct User
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{
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pub str& name,
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i32 age, // private
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}
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@@ -29,12 +32,14 @@ struct User {
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### Enums
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```mist
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pub enum Option<T> {
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pub enum Option<T>
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{
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Some(T),
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None,
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}
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pub enum Message {
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pub enum Message
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{
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Quit,
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Move(i32, i32),
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Write { str& content, i32 length },
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@@ -7,11 +7,13 @@ icon: Puzzle
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### Traits
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```mist
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pub trait Drawable {
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pub trait Drawable
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{
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void draw(&self);
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}
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pub trait Comparable<T> : Eq {
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pub trait Comparable<T> : Eq
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{
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i32 cmp(&self, T other);
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}
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```
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@@ -19,7 +21,8 @@ pub trait Comparable<T> : Eq {
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Trait requirements are specified after `:`:
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```mist
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trait MyTrait : SuperTrait + OtherTrait {
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trait MyTrait : SuperTrait + OtherTrait
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{
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void required_method(&self);
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void another(&self);
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}
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@@ -28,15 +31,18 @@ trait MyTrait : SuperTrait + OtherTrait {
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### Impl Blocks
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```mist
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impl MyType {
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impl MyType
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{
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void method(&self) { }
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}
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impl Trait for MyType {
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impl Trait for MyType
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{
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void method(&self) { }
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}
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impl<T> GenericTrait<T> for MyType {
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impl<T> GenericTrait<T> for MyType
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{
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void method(&self, T value) { }
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}
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```
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@@ -11,9 +11,10 @@ The semantic checker (`semantics.rs`) performs class field initialization analys
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The primary semantic check ensures all class fields are initialized in the constructor:
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```mist
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class Player {
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i32 health,
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str& name,
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class Player
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{
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i32 health;
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str& name;
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pub constructor(str& name)
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{
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@@ -21,8 +21,9 @@ The transpiler (`transpiler.mist` in `mist_api`) orchestrates the full pipeline.
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The `Module` struct represents the file-to-module mapping:
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```rust
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pub class Module {
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```mist
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pub class Module
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{
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pub String name;
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pub PathBuf path;
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pub Vec<Module> children;
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