OK I neglected to read the original post fully. My last post example would be based on allowing `const` and `let` declarations to expressions in of themselves (in the case of multi variables, returning the last one). So let me ask, what exactly would be the problem with this?
On Wed, 21 Mar 2018 at 12:20 Naveen Chawla <[email protected]> wrote: > What would `if.value` look like in an example? > > Wouldn't it be possible to have something like `if(const x = getX() && > const y = getY())` to capture more than just the conditional if required? > I'm guessing that would probably break something somewhere, but I'm not > sure what. > > On Wed, 21 Mar 2018 at 04:35 Jordan Harband <[email protected]> wrote: > >> Is the use case only ever to capture the thing that serves as the >> conditional? >> >> If so, would perhaps something like `if.value` work better? Since it's a >> keyword, it could be made to only work in the `if` block, and you wouldn't >> need any of that odd multi-statement stuff in the conditional parens. >> >> On Tue, Mar 20, 2018 at 12:57 PM, Rodrigo <[email protected]> wrote: >> >>> Proposal: inline let/const statements to declare and initialize >>> variables within if statements, so that temporary variables exist only >>> within the if/else block scope. >>> >>> Reason: limits variable scope to the block where really needed, in >>> similar fashion to variables defined in for(;;) statements. This >>> improves readability while reducing unnecessary variables roaming >>> outside their needed block. >>> >>> The syntax would be very similar to the for(;;) assignment/test pair: >>> >>> if (let x = 100; x > 50) { >>> console.log(x); // 100 >>> } >>> console.log(x); // ReferenceError >>> >>> // same for const >>> if( const x = foo(); typeof x === 'object' ) { >>> //... >>> } >>> >>> // the variable is available within any else block >>> // after its declaration >>> if (let x = foo(); x < 50) { >>> console.log(x); // y is not available here >>> } else if (let y = bar(); y > 0) { >>> console.log(x, y); >>> } else { >>> console.log(x, y); >>> } >>> >>> Right now there isn't a way to limit a variable to the if block: >>> >>> let x = 100; >>> if (x > 50) { >>> console.log(x); >>> } >>> // x is in scope, but may not be needed beyond the if statement >>> console.log(x); >>> >>> // or a non-strict assignment, which also "leaks" scope >>> if( (x = 100) > 50 ) { >>> // ... >>> } >>> >>> There are many "workarounds" available, here's a few: >>> >>> // workaround 1: can be remedied with a scope block >>> // but it's asymmetrical and non-idiomatic >>> { >>> let x = 100; >>> if (x > 50) { >>> console.log(x); >>> } >>> } >>> >>> // workaround 2: with a for statement >>> // but this is non-idiomatic, hard to read and error-prone >>> for (let x = 100; x > 50;) { >>> console.log(x); >>> break; >>> } >>> >>> If-initialization is available in many languages (Go, Perl and Ruby >>> come to mind) and are considered best practice in each one of them: >>> >>> // Golang - x is defined, assigned and conditionally tested >>> if x := 100; x > 50 { >>> // x is in scope here >>> } else { >>> // and in here >>> } >>> // x is not available here >>> >>> ###### Perl >>> if( my $x = 100 ) { >>> print $x; >>> } >>> print $x; # an error >>> >>> if ( ( my $x = myfoo() ) > 50 ) { # also ok in Perl >>> print $x; >>> } >>> >>> ###### Ruby >>> if ( x = 100 ) # parens required per style guide >>> puts(x) >>> end >>> puts(x) # unfortunately Ruby does not limit scope to if, so x "leaks" >>> >>> I think this would be a great and important addition to the language. >>> >>> -Rodrigo >>> >>> PS: Just for the sake of comparison, Perl-style if-assignments could >>> also be an >>> option, albeit a very bad one IMO: >>> >>> if( ( let x = 100 ) > 50 ) { >>> } >>> >>> A Perl-style, value-returning let/const has readability issues, opens >>> quite a few fronts and sort of implies that let/const can return >>> values anywhere in the code outside if/else. On the other hand it >>> would fit with the currently if assignment if( x = y ). Definitely not >>> recommended. >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> >
_______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
