Ok, weird proposal: Make the per-iteration update part of a for loop change
from "assignment to assignment or boolean expression" to allow:
*while COND do {...}:*
for i:=0; x[i]<4; {...}
*do {...} while COND:*
for i:= 0; ; x[i]<4 { ...}
On Wed, May 2, 2018 at 12:33 PM Louki Sumirniy <
louki.sumirniy.stal...@gmail.com> wrote:
> It adds absolutely nothing, that's why it should not be accepted. It will
> lead to a divergence in the way it's used as well. However I think maybe
> run block once before first condition check would be a useful and powerful
> addition. Maybe it shows my age that I even know what do-while
> post-conditional loops are, and why they are useful. I have had to write
> these more wordy constructs for exactly this purpose several times in a
> project I am working on.
>
> If there could be some less verbose way to flag that the condition only be
> checked first run. As I am thinking about it I am thinking of some other
> ways too, such as adding an or clause in the conditional that only checks
> if it's the first run, since golang's and and or operators are just
> drop-throughs, well, more or less, I mean, the or operator just does both
> tests and runs the block directly if the first condition passes. Here's a
> rough sketch of it while I am thinking about it
>
> for w:= true; w || <cond>; w=false {
> ...
> }
>
> This will always run the first time and I can't be certain but I think
> that the compiler may skip the assignment second time since it is an
> assignment. Still wordy but it is a do-while loop, nevertheless. If the
> assignment is repeated each time it's still an overhead cost, however. Some
> kind of 'do this only once' hint to the compiler maybe. But you see what I
> mean. This is definitely a case of something Go could use as an improvement
> and if it was constructed correctly it would not break old code, but
> instead actually give people a way to improve it when refactoring later on.
>
> On Wednesday, 2 May 2018 20:43:11 UTC+3, Ian Lance Taylor wrote:
>>
>> On Wed, May 2, 2018 at 2:48 AM, Hugh Fisher <hugo....@gmail.com> wrote:
>> >
>> > On Tuesday, May 1, 2018 at 10:45:30 PM UTC+10, Ian Lance Taylor wrote:
>> >>
>> >>
>> >> A `while` statement would presumably be exactly identical to a `for`
>> >> statement with a single condition. So adding a `while` statement
>> >> would not add any power to the language, and would add an additional
>> >> keyword. All language choices are a cost benefit decision. In this
>> >> case the benefit is a looping construct that some people will find
>> >> clearer to read and write, and the cost is a new keyword that
>> >> everybody needs to learn, and that at this point in the language's
>> >> evolution will likely break some, even if not much, existing code. I
>> >> don't think the benefit is worth the cost.
>> >>
>> > As for not adding any power, that's why I mentioned if-then-else and
>> switch.
>> > Switch with boolean cases is the same as if then else. It's not an
>> obscure
>> > side effect either, the Go Tour cheerfully explains how to use it
>> instead of
>> > if-then-else if you prefer.
>>
>> That is not the same thing, though. Yes, if-then-else and switch do
>> similar things, but they have a different syntax and are idiomatically
>> used in different ways. You can consider if-then-else as syntactic
>> sugar for switch, if you like. It's OK for a language to have some
>> syntactic sugar.
>>
>> But in this case you seem to be suggesting that we add `while <cond> {
>> <body> }` as an exact duplicate of the existing language construct
>> `for <cond> { <body> }`. That's not syntactic sugar. You are
>> suggesting that `while` just be a synonym for `for`. We don't need
>> two different keywords that mean exactly the same thing.
>>
>>
>> > Hmm, think I will have a look at the formal change proposal process...
>>
>> I encourage proposals but I can tell you upfront that this proposal
>> will not be accepted.
>>
>> Ian
>>
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Michael T. Jones
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