1 stable release
1.0.0 | Apr 16, 2021 |
---|
#15 in #python-3
Used in fstrings-rust
12KB
284 lines
::fstrings
-
Note, this crate has been rendered obsolete as of 1.58.0, wherein
let x = 42; println!("{x}");
acts aslet x = 42; println_f!("{x}");
here.A precursor/pioneer crate, for sure, and one which now has been subsumed by RFC 2795, which successfully championed the ideas behind this crate! 🏆
Basic fstring interpolation in Rust
The interpolation works as follows:
-
if the (template) string literal contains a named parameter (e.g.
{name}
) -
and no
name = value
argument is fed to the formatting call, -
then an automatic
name = name
argument is added, so that the variable is effectively interpolated from the current scope.
Example
#[macro_use]
extern crate fstrings;
fn main ()
{
let name = "World";
// Usage is simple: just append `_f` to the name of any formatting macro
println_f!("Hello, {name}!");
assert_eq!(
f!("Hello, {name}!"), // shorthand for String creation (Python-like)
String::from("Hello, World!"),
);
// ## Advanced cases:
{
// It remains compatible with classic formatting parameters
assert_eq!(
f!("{hi}, {name}!", hi = "Hello"),
"Hello, World!",
);
// You can override / shadow the named arguments
assert_eq!(
f!("Hello, {name}!", name = "Earth"),
"Hello, Earth!",
);
// You can use field access (but no method calls!)
let foo = Foo { name }; /* where */ struct Foo<T> { name: T }
assert_eq!(
f!("Hello, {foo.name}!"),
"Hello, World!",
);
// This also works with tuple indexing.
let ft_and_name = (42, name);
assert_eq!(
f!("Hello, {ft_and_name.1}!"),
"Hello, World!",
);
// You can use fstrings to debug by appending a `=` after the
// interpolated expression.
let x = 0b_101010;
assert_eq!(
f!("In this context {x=}"),
"In this context x = 42",
);
}
}
Dependencies
~1.5MB
~37K SLoC