Macro quote::format_ident
source · macro_rules! format_ident { ($fmt:expr) => { ... }; ($fmt:expr, $($rest:tt)*) => { ... }; }
Expand description
Formatting macro for constructing Ident
s.
§Syntax
Syntax is copied from the format!
macro, supporting both positional and
named arguments.
Only a limited set of formatting traits are supported. The current mapping of format types to traits is:
{}
⇒IdentFragment
{:o}
⇒Octal
{:x}
⇒LowerHex
{:X}
⇒UpperHex
{:b}
⇒Binary
See std::fmt
for more information.
§IdentFragment
Unlike format!
, this macro uses the IdentFragment
formatting trait by
default. This trait is like Display
, with a few differences:
IdentFragment
is only implemented for a limited set of types, such as unsigned integers and strings.Ident
arguments will have theirr#
prefixes stripped, if present.
§Hygiene
The Span
of the first Ident
argument is used as the span of the final
identifier, falling back to Span::call_site
when no identifiers are
provided.
// If `ident` is an Ident, the span of `my_ident` will be inherited from it.
let my_ident = format_ident!("My{}{}", ident, "IsCool");
assert_eq!(my_ident, "MyIdentIsCool");
Alternatively, the span can be overridden by passing the span
named
argument.
let my_span = /* ... */;
format_ident!("MyIdent", span = my_span);
§Panics
This method will panic if the resulting formatted string is not a valid identifier.
§Examples
Composing raw and non-raw identifiers:
let my_ident = format_ident!("My{}", "Ident");
assert_eq!(my_ident, "MyIdent");
let raw = format_ident!("r#Raw");
assert_eq!(raw, "r#Raw");
let my_ident_raw = format_ident!("{}Is{}", my_ident, raw);
assert_eq!(my_ident_raw, "MyIdentIsRaw");
Integer formatting options:
let num: u32 = 10;
let decimal = format_ident!("Id_{}", num);
assert_eq!(decimal, "Id_10");
let octal = format_ident!("Id_{:o}", num);
assert_eq!(octal, "Id_12");
let binary = format_ident!("Id_{:b}", num);
assert_eq!(binary, "Id_1010");
let lower_hex = format_ident!("Id_{:x}", num);
assert_eq!(lower_hex, "Id_a");
let upper_hex = format_ident!("Id_{:X}", num);
assert_eq!(upper_hex, "Id_A");