Reviewing feedback on patterns in switch

[Brian Goetz]

>>
>> For me, && is more natural than "when" because i've written more 
>> switch that uses && than "when".
>> And don't forget that unlike most of the code, with pattern matching 
>> the number of characters does matter, this is more similar to 
>> lambdas, if what you write is too verbose, you will not write it.
>
> At the risk of premature bikeshedding, have we already discussed and 
> discarded the idea of spelling “when” as “if”? It’s been a long time, 
> and I forget.

There was not extensive discussion on this, and its all very 
subjective/handwavy/"what we think people would think", but I remember a 
few comments on this:

  - The generality of "if" reminded people of the Perl-style "statement 
unless condition" postfix convention, and that people might see it as an 
"inconsistency" that they could not then say

    x = 3 if (condition);

which is definitely somewhere we don't want to go.


  - We're use to seeing "if" with a consequence, and a "naked" if might 
have the effect of "lookahead pollution" in our mental parsers.


  - Keeping `if` for statements allows us to keep the "body" of case 
clauses visually distinct from the "envelope":

     case Foo(var x)
     if (x > 3) : if (x > 10) { ... }

would make people's eyes go buggy.  One could argue that "when" is not 
fantastically better:

     case Foo(var x)
     when (x > 3) : if (x > 10) { ... }

but it doesn't take quite as long to de-bug oneself in that case.

On 2/15/2022 9:55 PM, Guy Steele wrote:
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