Method generateMatchSwitchWithAssignment

pkg/codegen/match.go:841–889

generateMatchSwitchWithAssignment generates switch statement that assigns to varName. Example: switch x.(type) { case A: varName = "a"; case B: varName = "b" } Includes default panic with scrutinee value.

(varName string)

// Example: switch x.(type) { case A: varName = "a"; case B: varName = "b" }
// Includes default panic with scrutinee value.
func (g *MatchCodeGen) generateMatchSwitchWithAssignment(varName string) {
	// Generate scrutinee
	scrutineeResult := GenerateExpr(g.Match.Scrutinee)
	scrutineeCode := string(scrutineeResult.Output)

	// CRITICAL FIX: Always bind match value to temp var to prevent double evaluation
	// This prevents side-effect functions (e.g., popQueue()) from executing twice:
	// once in switch condition and once in panic clause
	scrutineeTempVar := g.SharedTempVar("val")
	g.Write(fmt.Sprintf("%s := %s\n", scrutineeTempVar, scrutineeCode))

	// Check if we need type assertion (for constructor patterns)
	needsTypeSwitch := g.hasConstructorPatterns()

	// Check if we have any bindings (to decide on temp var usage)
	hasBindings := g.hasBindings()

	if needsTypeSwitch {
		// Generate type switch: switch v := scrutinee.(type) or switch scrutinee.(type)
		if hasBindings {
			// Need temp var for bindings
			tempVar := g.SharedTempVar("v")
			g.scrutineeTempVar = tempVar // Store for generateArmBodyWithAssignment
			g.Write("switch " + tempVar + " := ")
			g.Write(scrutineeTempVar)
			g.Write(".(type) {\n")
		} else {
			// No bindings - just use scrutinee.(type) without variable
			g.Write("switch ")
			g.Write(scrutineeTempVar)
			g.Write(".(type) {\n")
		}
	} else {
		// Generate value switch: switch scrutinee {
		g.Write("switch ")
		g.Write(scrutineeTempVar)
		g.Write(" {\n")
	}

	// Group arms by pattern type to avoid duplicate case clauses
	// This handles guarded patterns correctly
	g.generateGroupedCasesWithAssignment(varName, needsTypeSwitch)

	// NO DEFAULT PANIC:
	// - Expression matches: verified exhaustive by checkExhaustiveness()
	// - Statement matches: silent fall-through per user requirement

	g.WriteByte('}')
}

// generateMatchArmWithAssignment generates a case clause with assignment to varName.
// Handles pattern matching, guards, and assignment generation.