v01

thirdparty/CLI11/book/chapters/validators.md

@@ -0,0 +1,64 @@
+# Validators
+
+There are two forms of validators:
+
+* `transform` validators: mutating
+* `check` validators: non-mutating (recommended unless the parsed string must be mutated)
+
+A transform validator comes in one form, a function with the signature `std::string(std::string)`.
+The function will take a string and return the modified version of the string. If there is an error,
+the function should throw a `CLI::ValidationError` with the appropriate reason as a message.
+
+However, `check` validators come in two forms; either a simple function with the const version of the
+above signature, `std::string(const std::string &)`, or a subclass of `struct CLI::Validator`. This
+structure has two members that a user should set; one (`func_`) is the function to add to the Option
+(exactly matching the above function signature, since it will become that function), and the other is
+`name_`, and is the type name to set on the Option (unless empty, in which case the typename will be
+left unchanged).
+
+Validators can be combined with `&` and `|`, and they have an `operator()` so that you can call them
+as if they were a function. In CLI11, const static versions of the validators are provided so that
+the user does not have to call a constructor also.
+
+An example of a custom validator:
+
+```cpp
+struct LowerCaseValidator : public Validator {
+    LowerCaseValidator() {
+        name_ = "LOWER";
+        func_ = [](const std::string &str) {
+            if(CLI::detail::to_lower(str) != str)
+                return std::string("String is not lower case");
+            else
+                return std::string();
+        };
+    }
+};
+const static LowerCaseValidator Lowercase;
+```
+
+If you were not interested in the extra features of Validator, you could simply pass the lambda function above to the `->check()` method of `Option`.
+
+The built-in validators for CLI11 are:
+
+| Validator           | Description |
+|---------------------|-------------|
+| `ExistingFile`      | Check for existing file (returns error message if check fails) |
+| `ExistingDirectory` | Check for an existing directory (returns error message if check fails) |
+| `ExistingPath`      | Check for an existing path |
+| `NonexistentPath`   | Check for an non-existing path |
+| `Range(min=0, max)` |  Produce a range (factory). Min and max are inclusive. |
+
+
+And, the protected members that you can set when you make your own are:
+
+| Type | Member | Description |
+|------|--------|-------------|
+| `std::function<std::string(std::string &)>` | `func_` | Core validation function - modifies input and returns "" if successful |
+| `std::function<std::string()>` | `desc_function` | Optional description function (uses `description_` instead if not set) |
+| `std::string` | `name_` | The name for search purposes |
+| `int` (`-1`) | `application_index_` | The element this validator applies to (-1 for all) |
+| `bool` (`true`) | `active_` | This can be disabled |
+| `bool` (`false`) | `non_modifying_` | Specify that this is a Validator instead of a Transformer |
+
+