Running the same commands just inside src/librustc (which is essentially
client code) gives:
let mut = 1051
let (no mut) = 5752
So the ratio is even more skewed toward immutable lets, and, librustc is
written in "old" Rust, so I can only see the ratio moving away from let
mut even more: e.g. there are still instances of patterns like `let mut
v = ~[]; for x in iter { v.push(x); }` rather than just `let v =
iter.collect();`.
(Obviously those grep commands give a very simplistic view, but I think
it's accurate enough to demonstrate that `let mut` is not the common case.)
On 30/01/14 14:18, Samuel Williams wrote:
Do you think for client code it would be the same proportion as in
"library" code?
On 30 January 2014 16:13, Huon Wilson <[email protected]
<mailto:[email protected]>> wrote:
On 30/01/14 14:09, Samuel Williams wrote:
I agree that it is syntactic salt and that the design is to
discourage mutability. I actually appreciate that point as a
programmer.
w.r.t. this specific issue: I think what concerns me is that it
is quite a high burden for new programmers (I teach COSC1xx
courses to new students so I have some idea about the level of
new programmers). For example, you need to know more detail about
what is going on - new programmers would find that difficult as
it is one more concept to overflow their heads.
Adding "var" as a keyword identically maps to new programmer's
expectations from JavaScript. Writing a program entirely using
"var" wouldn't cause any problems right? But, could be optimised
more (potentially) if using "let" for immutable parts.
Anyway, I'm not convinced either way, I'm not sure I see the
entire picture yet. But, if I was writing code, I'd certainly get
sick of writing "let mut" over and over again - and looking at
existing rust examples, that certainly seems like the norm..
Inside the main rust repository:
$ git grep 'let ' -- '*.rs' | grep -v mut | wc -l
17172
$ git grep 'let ' -- '*.rs' | grep mut | wc -l
5735
i.e. there are approximately 3 times more non-mutable variable
bindings than there are mutable ones.
On 30 January 2014 15:59, Samuel Williams
<[email protected]
<mailto:[email protected]>> wrote:
I guess the main gain would be less typing of what seems to
be a reasonably common sequence, and the formalisation of a
particular semantic pattern which makes it easier to
recognise the code when you visually scanning it.
On 30 January 2014 15:50, Kevin Ballard <[email protected]
<mailto:[email protected]>> wrote:
On Jan 29, 2014, at 6:43 PM, Brian Anderson
<[email protected] <mailto:[email protected]>> 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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