"var" as explicit non-final marker

Michael Hendricks

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Oct 26, 2011, 9:41:25 PM10/26/11

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Proposal:

Allow "var" before any type declaration as an explicit statement that the developer intends the variable to be non-final. The presence of "var" before a type has no effect on the program's behavior because it only declares what is already the default. The "var" is only there to document developer intent and for future static analysis tools.

If I've read the spec correctly, I intend section 5 to have the following, modified definition:

finalVarOrType:

final type? |

var type? |

type

;

Motivation:

Some developers prefer to work with single-assignment variables, but manually marking each variable as final is a burden. Making all variables final by default burdens other developers (see earlier discussions[1][2]). Without changes to Dart, "final-ists" could write a static analysis tool to warn about multiple-assignment:

int x = 7;

int y = 1;

x = x + y; // tool warns: multiple assignment to variable "x"

Without this proposal, the tool could use special comments to exempt specific variables from the restriction.

int x = 7; /* {non-final} */

With this proposal, the developer accomplishes the same thing with

var int x = 7;

Since all existing Dart code is still valid under this proposal, I can't see any additional burden for developers coming from Java/JS/C#. Developers wanting to enforce single-assignment carry the burden of their own preference since they have to write the static analysis tool (or compiler option).

Any thoughts or questions? Is such a change acceptable?

[1]: https://groups.google.com/a/dartlang.org/group/misc/browse_thread/thread/8ff8f9c99505f6d9

[2]: https://groups.google.com/a/dartlang.org/group/misc/browse_thread/thread/a082e72f06f9bcc9

--

Michael