Skip to content

Composing validators

Sometimes the conditions you want to impose are more complex than a simple minimum or a simple regex pattern. That is why reflect-cpp allows you to compose them using the operators rfl::AnyOf, rfl::AllOf and rfl::OneOf.

  • rfl::AnyOf requires that at least one of the conditions contained therein be true. It thus works like an OR operator.
  • rfl::AllOf requires that all of the conditions contained therein be true. It thus works like an AND operator.
  • rfl::OneOf requires that exactly one of the conditions contained therein be true. It thus works like a XOR operator.

For instance, if you want to ensure that a person's age is a reasonable number, you can impose two conditions as follows:

using Age = rfl::Validator<int,
                           rfl::AllOf<rfl::Minimum<0>, rfl::Maximum<130>>>;

struct Person {
  rfl::Rename<"firstName", std::string> first_name;
  rfl::Rename<"lastName", std::string> last_name;
  Age age;
};

However, if you pass more than one constraint to rfl::Validator, they will be automatically connected using rfl::AllOf, so you might as well write:

using Age = rfl::Validator<int, rfl::Minimum<0>, rfl::Maximum<130>>;

...

You can also nest composed validators. For instance, in this case the age must either be 0-10 or 40-130.

using Age = rfl::Validator<
    int,
    rfl::AnyOf<rfl::AllOf<rfl::Minimum<0>, rfl::Maximum<10>>,
               rfl::AllOf<rfl::Minimum<40>, rfl::Maximum<130>>>>;

You can also compose regex patterns:

using TableOrColumnName = rfl::Validator<
    std::string,
    rfl::AnyOf<rfl::PatternValidator<R"(^[A-Z]+(?:_[A-Z]+)*$)", "TableName">,
               rfl::PatternValidator<R"(^[a-z]+(?:_[a-z]+)*$)", "ColumnName">>>;