Symbol constructor Null safety

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.