Macro quote::format_ident [−][src]
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:
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");