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content/docs/internals/semantic-analysis.mdx

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+---
+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.