[rust-dev] "let mut" <-> "var"

Kevin Ballard kevin at sb.org
Wed Jan 29 18:50:27 PST 2014


On Jan 29, 2014, at 6:43 PM, Brian Anderson <banderson at mozilla.com> wrote:

> On 01/29/2014 06:35 PM, Patrick Walton wrote:
>> On 1/29/14 6:34 PM, Samuel Williams wrote:
>>> Perhaps this has been considered already, but when I'm reading rust code
>>> "let mut" just seems to stick out all over the place. Why not add a
>>> "var" keyword that does the same thing? I think there are lots of good
>>> and bad reasons to do this or not do it, but I just wanted to propose
>>> the idea and see what other people are thinking.
>> 
>> `let` takes a pattern. `mut` is a modifier on variables in a pattern. It is reasonable to write `let (x, mut y) = ...`, `let (mut x, y) = ...`, `let (mut x, mut y) = ...`, and so forth.
>> 
>> Having a special "var" syntax would defeat this orthogonality.
> 
> `var` could potentially just be special-case sugar for `let mut`.

To what end? Users still need to know about `mut` for all the other uses of patterns. This would reserve a new keyword and appear to duplicate functionality for no gain.

-Kevin
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