const or immutable?

[Ali Çehreli]

On 9/22/21 1:17 PM, Adam D Ruppe wrote:
 > On Wednesday, 22 September 2021 at 20:06:59 UTC, Ali Çehreli wrote:
 >> tl;dr Do you use 'const' or 'immutable' by-default for parameters and
 >> for local data?
 >
 > well i often ignore it but `const` (or often better yet, `inout` if
 > there's any relation to a member of yours or if you return it)

'inout' has been useful in cases like you mention. For example, a 
slice's elements should reflect the mutability of 'this'. I am mostly 
interested in revising a beginner-oriented chapter, where 'inout' 
doesn't exist yet.

 > is better
 > on function arguments, and `immutable` is better on internal members.
 >
 > The exception is when you are storing something from someone else, where
 > immutable params might be more important.

I noticed that as well: For example, if a file name constructor 
parameter is string, I don't need to copy the file name to a member. 
(This actually appears later in the book where I realize constructor 
arguments might better be 'immutable'.)

 > But if you are looking and not
 > touching, const or `in` is good.

'in' has been another question: It appears a lot in my book but I almost 
never use it myself. Perhaps that's the answer? I would like that. 
However, the proposed change of meaning of 'in' is also worrying but I 
think it will strenghthen the case for it's use I guess.

 >> Aside: If 'const' is welcoming, why do we type 'string' for string
 >> parameters when we don't actually *require* immutable:
 >
 > Unfortunate naming here... the convenient name encourages its use but it
 > is indeed often suboptimal.

I agree. However, ironically and worryingly :), it just works most of 
the time.

Ali