Supporting Ruby 1.9's hash syntax in Ruby 1.8 - ruby

Question

I'm writing a Ruby gem using the {key: 'value'} syntax for hashes throughout my code. My tests all pass in 1.9.x, but I (understandably) get syntax error, unexpected ':', expecting ')' in 1.8.7.
Is there a best practice for supporting the 1.8.x? Do I need to rewrite the code using our old friend =>, or is there a better strategy?

Answer 1

I think you're out of luck, if you want to support 1.8 then you have to use =>. As usual, I will mention that you must use => in certain cases in 1.9:
If the key is not a symbol. Remember that any object (symbols, strings, classes, floats, ...) can be a key in a Ruby Hash.
If you need a symbol that you'd quote: :'this.that'.
If you use MongoDB for pretty much anything you'll be using things like :$set => hash but $set: hash is a syntax error.
Back to our regularly scheduled programming.
Why do I say that you're out of luck? The Hash literal syntaxes (both of them) are hard-wired in the parser and I don't think you're going to have much luck patching the parser from your gem. Ruby 1.8.7's parse.y has this to say:
assoc : arg_value tASSOC arg_value
{
$$ = list_append(NEW_LIST($1), $3);
}
;
and tASSOC is => so hash literals are hard-wired to use =>. 1.9.3's says this:
assoc : arg_value tASSOC arg_value
{
/*%%%*/
$$ = list_append(NEW_LIST($1), $3);
/*%
$$ = dispatch2(assoc_new, $1, $3);
%*/
}
| tLABEL arg_value
{
/*%%%*/
$$ = list_append(NEW_LIST(NEW_LIT(ID2SYM($1))), $2);
/*%
$$ = dispatch2(assoc_new, $1, $2);
%*/
}
;
We have the fat-arrow syntax again (arg_value tASSOC arg_value) and the JavaScript style (tLABEL arg_value); AFAIK, tLABEL is also the source of the restrictions on what sorts of symbols (no :$set, no :'this.that', ...) can be used with the JavaScript-style syntax. The current trunk parse.y matches 1.9.3 for Hash literals.
So the Hash literal syntax is hard-wired into the parser and you're stuck with fat arrows if you want to support 1.8.

Answer 2

Ruby 1.8.7 does not support the new hash syntax.
If you desperately need hash syntax on the non-YARV c-based implementation of Ruby, there is a totally unsupported 1.8 head branch, so you can do
rvm install ruby-head --branch ruby_1_8 ; rvm ruby-head
ruby -v
ruby 1.8.8dev (2011-05-25) [i386-darwin10.7.0]
but upgrading to 1.9 is the way to go.