Is it possible to create custom literals using Rust macros?

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Yes, it is possible to create custom literals using Rust macros. Rust macros allow you to define new language constructs or modify existing ones.

For example, to create a custom integer literal that multiplies its value by 2, you can define a macro like this:

macro_rules! double {
    ($x:expr) => {
        $x * 2
    };
}

let x = double!(10);

In this example, the double! macro takes an expression as its argument, and multiplies its value by 2. The resulting value is then assigned to the variable x.

You can also define custom string literals using macros. For example, to create a custom string literal that converts all its characters to uppercase, you can define a macro like this:

macro_rules! upper {
    ($s:expr) => {
        $s.to_uppercase().to_string()
    };
}

let s = upper!("hello");

In this example, the upper! macro takes a string expression as its argument, converts all its characters to uppercase using the to_uppercase method of the String type, and returns the resulting uppercase string.

Overall, Rust macros provide a powerful mechanism for extending the language with custom constructs and literals.