格式化字符串

The String Formatter is a utility that allows you to customize the formatting of strings in Valkyrie programming language.

It provides various options to format strings based on different parameters.

`{v}`

The {v} placeholder is used to insert the value of variable v into a string. It is equivalent to calling v.display().

"{v}" // v.display()

To explicitly initialize the string with the default formatter, it is recommended to add f before the string.

f"{v}"   // v.display()

`{v:formatter}`

The {v:formatter} syntax allows you to specify a custom formatter for the variable v. This enables you to format the value according to specific rules or patterns.

"{v:?}" // v.display("?")

For example, you can format a DateTime object to display the date and time in a specific format.

let time = DateTime("2020-02-29 20:02:29");
"{time:dd.MM.yyyy HH:mm:ss}"
// Output: 02.29.2020 20:02:29

Alternatively, you can use the display function of the DateTime object to achieve the same result.

time.display("dd.MM.yyyy HH:mm:ss")

`{v, ...arguments}`

The {v, ...arguments} syntax allows you to provide additional arguments to the formatter. This can be useful when you need to specify formatting options such as culture or locale.

let time = DateTime("2020-02-29 20:02:29");
"{time, 'dd.MM.yyyy HH:mm:ss', culture: 'en-US'}"
// Output: 02/29/2020 20:02:29

In the above example, the culture argument is used to format the date and time according to the English (United States) locale.

You can achieve the same result by calling the display function of the DateTime object and providing the desired formatting options.

time.display("%Y-%m-%d %H:%M:%S", culture: 'en-US')

Formatter

The Display trait provides the underlying implementation for formatting.

It defines the following methods:

trait ToString {
    format(self, mut formatter: Formatter, ...args): Result<(), DisplayError>;
    #hide(completion)
    format_hint(self): u64 { 0 }
    final display(self, ...args) {
        let mut f = Formatter(UTF8Text(capacity: self.format_hint()));
        self.format(f)
        f.buffer
    }
}

The format method is responsible for formatting the value and writing it to the formatter object.
- It takes the value itself (self) and additional formatting arguments (args).
- It returns a Result indicating whether the formatting was successful or not.
The format_hint method provides a hint about the expected capacity of the formatter.
- This can be useful for optimizing memory allocation when formatting large strings.
The display method is a convenience function that initializes a Formatter object, calls format on the value, and returns the formatted string as a buffer.

By implementing the Display trait and providing custom formatting logic, you can customize the display of objects in Valkyrie.

Formatter Derive

The Formatter Derive feature in Valkyrie allows you to automatically generate the implementation of the Display trait for a custom class or structure. This eliminates the need to manually implement the format method for formatting the object's display.

To use the Formatter Derive, you need to annotate your class or structure with #derive(Display). This tells the Valkyrie compiler to generate the necessary code for formatting the object.

Here's an example of using the Formatter Derive for a Point class:

#derive(Display)
class Point {
    x: f64,
    y: f64,
}

With the #derive(Display) annotation, the Valkyrie compiler will automatically generate the implementation of the Display trait for the Point class. This implementation will include the format method, which formats the object's display based on the provided formatting options.

After applying the Formatter Derive to the Point class, you can use the display function or the {} placeholder to format and display Point objects.

let p = new Point { x: 2.5, y: 3.7 };
f"{p}"  // Output: "Point { x: 2.5, y: 3.7 }"

The generated implementation of the Display trait will use the default formatting options for the class members. If you want to customize the formatting, you can override the format method in your class and provide your own logic.

By using the Formatter Derive, you can simplify the implementation of the Display trait for your custom classes and structures, making it easier to format and display objects in a desired way.

# 格式化字符串

# {v}

# {v:formatter}

# {v, ...arguments}