description

# Symbol constructor Null safety

const Symbol(

1. 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;