Module pattern_gen 

Pattern matching generation from tag checks (DECY-082).

Transforms C tagged union access patterns (if-else-if chains checking tag fields) into safe Rust match expressions with exhaustive pattern matching.

Transformation

C code:

if (v.tag == INT) {
    return v.data.i;
} else if (v.tag == FLOAT) {
    return v.data.f;
} else {
    return -1;
}

Rust code:

match v {
    Value::Int(i) => return i,
    Value::Float(f) => return f,
    _ => return -1,
}

Benefits

• Type safety: Compiler verifies correct variant access
• Exhaustiveness: All possible cases must be handled
• Zero unsafe: No unsafe union field access
• Pattern binding: Direct access to variant payloads

Structs

PatternGenerator

Generator for Rust pattern matching from C tag checks.