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  • Another switch

Another switch

# Giacomo Cau (12 years ago)

I wish to submit a little proposal.

Today the switch statement has an explicit break at the end of the statement and an implicit continue to the next case

but this break is very boring and error prone.

Wouldn’t it be possible to think a switch that has an explicit continue to the next case and an implicit break at the end of the statement?

This is the hypothetical new statement syntax with a new keyword:

hctiws ( ... ) { ... }
select ( ... ) { ... }

or without a new keyword:

switch ( ... ) break { ... }

but with the current switch equals to

switch ( ... ) continue { ... }
# Nathan Wall (12 years ago)

Not sure whether this will be of interest to you, but I have been working on a JS-derived language called Proto (still highly experimental) which has a switch statement that works exactly as you described:

Nathan-Wall/proto/blob/master/docs/control/switch.md

Perhaps you will at least find it interesting. :)

Nathan

# Brendan Eich (12 years ago)

Definitely good to see new languages being designed and implemented.

JS is not going to break compatibility on the old fall-through behavior of switch, inherited from Java from C++ from C. All the C-like languages copy this flaw, because to do otherwise with the same keyword would be worse (confused users cross-training and -coding among languages would want our scalps), and IMHO using novel reserved words would be hardly better.

# Claude Pache (12 years ago)

Since the switch/case construct in Proto runs differently from the usual way, it should be spelt differently to avoid the confusion that will inevitably occur when switching between languages. For instance, Perl names it given/when 1, and SQL uses case/when.

# Giacomo Cau (12 years ago)

yes, so great it would be a pleasure to contribute :)

the proposal doesn't want, by no means, to break the compability with the present syntax and/or semantics of the switch. At most, should be considered as an extension of current syntax with a consequential new semantics.

the swith, as it is known, should anyhow be written as

switch (...) {
    case ...: ...; break;
    case ...: ...; break;
    case ...: ...;
    case ...: ...; break;
    otherwise: ...
}

but, it could be handy to write the same thing with a slightly different syntax:

switch (...) break {
    case ...: ...;
    case ...: ...;
    case ...: ...; continue;
    case ...: ...;
    otherwise: ...
}

Some break less, no new keyword, no incompatibility with past. Who shall use it, will know from the start that here, the continue will not lead him at the beginning of the first for or while that englobe the switch, but only at the following case.

Then, willingly, we could also think that normal switch be desugared in

switch (...) continue {
    case ...: ...; break;
    case ...: ...; break;
    case ...: ...;
    case ...: ...; break;
    otherwise: ...
}

with break and continue (except that between ')' and '{' ) that, obviously, continue as before. This isn't a must, it's just for my pleasure in finding regularity.

At last, if we were to look for the burden of a new keyword, even better

select (...) {
    case ...: ...;
    case ...: ...;
    case ...: ...; continue;
    case ...: ...;
    otherwise: ...
}

but I realize this could be a break point of the existing code and, onestly speaking, it is beyond my ability to evaluate.

# Eric Elliott (12 years ago)

Object literals are already a great alternative to switch in JS:

var cases = {
  val1:  function () {},
  val2: function () {}
};

cases[val]();

Fall through is more trouble than it's worth, IMO.

# Mathias Bynens (12 years ago)

In that case, you’d need a hasOwnProperty check to make sure you’re not trying to call __proto__ or toString, etc. See rwaldron/idiomatic.js/#misc for a more complete example.

# Nick Krempel (12 years ago)

Also only works when you're switching on something with a meaningful conversion to string.

# Rick Waldron (12 years ago)

On Fri, Feb 21, 2014 at 7:55 AM, Nick Krempel <ndkrempel at google.com> wrote:

Also only works when you're switching on something with a meaningful conversion to string.

On 20 Feb 2014, at 21:20, Eric Elliott <eric at ericleads.com> wrote:

Object literals are already a great alternative to switch in JS:

Right, this wouldn't work if the "case" wanted object references, but it would work nicely with Symbols.

# Eric Elliott (12 years ago)

In practice, I find that everything converts nicely to a string when you precede it with a ternary assignment.

I also find that when you do that, it's pretty trivial to control what those strings are, which makes hasOwnProperty superfluous.

I haven't used a switch in JavaScript for quite a few years now, and I don't miss it at all.

# C. Scott Ananian (12 years ago)

In the ES6 world, you should probably set up a Map for your switch statement; that would allow you to easily use non-string cases.