Function castUnion

src/cpp-syntax-utils.ts:200–226

(expr: Expression, target: Type, source: Type)

 * Conversions involving unions.
 */
export function castUnion(expr: Expression, target: Type, source: Type): Expression {
  // From non-union to union.
  if (source.category != 'union' && target.category == 'union') {
    // Convert undefined to std::monostate.
    if (source.category == 'undefined')
      return new CustomExpression(target, (ctx) => 'std::monostate{}');
    // Find the target subtype and do an explicit conversion.
    const subtype = target.types.find(t => t.equal(source));
    if (!subtype)
      throw new Error(`The target union "${target.name}" does not contain the source type "${source.name}"`);
    return castExpression(expr, subtype);
  }
  // From union to non-union.
  if (source.category == 'union' && target.category != 'union') {
    const subtype = source.types.find(t => t.equal(target));
    if (!subtype) {
      // When casting to types like size_t, convert to double and try again.
      if (target.isNonJsPrimitive())
        return castUnion(expr, Type.createNumberType(), source);
      throw new Error(`The union "${source.name}" does not contain the target type "${target.name}"`);
    }
    return new CustomExpression(subtype, (ctx) => {
      return `std::get<${subtype.print(ctx)}>(${expr.print(ctx)})`;
    });
  }
  return expr;
}

/**
 * Conversions between optionals.