---
title: Semantic Analysis
description: Class field initialization verification and the GetMutability analysis system.
icon: SearchCheck
---

The semantic checker (`semantics.rs`) performs class field initialization analysis. When a class has a constructor, it verifies that every declared field is mutated (directly or indirectly via method calls) within the constructor body.

### Field Initialization

The primary semantic check ensures all class fields are initialized in the constructor:

```mist
class Player {
    i32 health,
    str& name,

    pub constructor(str& name)
    {
        self.name = name;
        // Error: field 'health' is uninitialized
    }
}
```

### How It Works

The `GetMutability` trait tracks which identifiers are mutated:

1. Collects all identifiers that get `&mut` references
2. Tracks `self.field = value` patterns
3. Follows method calls that might initialize fields (transitively)
4. Ensures all conditional branches initialize the same fields (intersection semantics)
5. `super` assignments count for `_super` field initialization

If any field is uninitialized after the analysis, a `SemanticError` is reported with the field's source position.