Symbol constructor Null safety
- String name
Constructs a new Symbol representing the provided name.
The name must be a valid public Dart member name, public constructor name, or library name, optionally qualified.
A qualified name is a valid name preceded by a public identifier name
and a '.', e.g., foo.bar.baz= is a qualified version of baz=.
That means that the content of the name String must be either
- a valid public Dart identifier
(that is, an identifier not starting with "
_"), - such an identifier followed by "=" (a setter name),
- the name of a declarable operator
(one of "
+", "-", "*", "/", "%", "~/", "&", "|", "^", "~", "<<", ">>", "<", "<=", ">", ">=", "==", "[]", "[]=", or "unary-"), - any of the above preceded by any number of qualifiers,
where a qualifier is a non-private identifier followed by '
.', - or the empty string (the default name of a library with no library name declaration).
Symbol instances created from the same name are equal,
but not necessarily identical, but symbols created as compile-time
constants are canonicalized, as all other constant object creations.
assert(new Symbol("foo") == new Symbol("foo"));
assert(identical(const Symbol("foo"), const Symbol("foo")));
If name is a single identifier that does not start with an underscore,
or it is a qualified identifier,
or it is an operator name different from unary-,
then the result of const Symbol(name) is the same instance that
the symbol literal created by prefixing # to the content of name
would evaluate to.
assert(new Symbol("foo") == #foo);
assert(new Symbol("[]=") == #[]=]);
assert(new Symbol("foo.bar") == #foo.bar);
assert(identical(const Symbol("foo"), #foo));
assert(identical(const Symbol("[]="), #[]=]));
assert(identical(const Symbol("foo.bar"), #foo.bar));
This constructor cannot create a Symbol instance that is equal to
a private symbol literal like #_foo.
const Symbol("_foo") // Invalid
The created instance overrides Object.==.
The following text is non-normative:
Creating non-const Symbol instances may result in larger output. If
possible, use MirrorsUsed from "dart:mirrors" to specify which names
might be passed to this constructor.
Implementation
const factory Symbol(String name) = internal.Symbol;