Function operator()

cpp/src/arrow/compute/expression_test.cc:1229–1237

struct {
  void operator()(Expression expr, Expression expected) {
    ASSERT_OK_AND_ASSIGN(expr, expr.Bind(*kBoringSchema));
    ASSERT_OK_AND_ASSIGN(expected, expected.Bind(*kBoringSchema));

    ASSERT_OK_AND_ASSIGN(auto folded, FoldConstants(expr));

    EXPECT_EQ(folded, expected);
    ExpectIdenticalIfUnchanged(folded, expr);
  }
} ExpectFoldsTo;

TEST(Expression, FoldConstants) {