Feature #13122
closedSpecial syntax for Hash#default_proc
Description
The current Hash#default_proc flow usually looks something like this:
my_hash = { key: "value" }
my_hash.default_proc = proc { |h, k| h[k] = "other value" }
This makes the common practice of freezing large constant hashes unwieldy. For example,
this:
MY_HASH = {
key: "value"
}.freeze
needs to become
MY_HASH = {
key: "value"
}
MY_HASH.default_proc = proc { |h, k| h[k] = "other value" }
MY_HASH.freeze
if a default_proc
is used.
I propose a new syntax for setting the default_proc within the hash-declaration itself:
my_hash = {
key: "value"
*: proc { |h, k| h[k] = "other value" }
}
*:
as a hash-key is currently a syntax error, so I think there's space in the language for this. Of course, this should also support rocket-style:
my_hash = {
"key" => "value"
* => proc { |h, k| h[k] = "other value" }
}
(I'm completely open to alternative syntaxes, *
just comes to mind because of wildcarding).
I'm happy to attempt work on this, if this feature is desired. I have experience with MRI's API, but not with writing new syntax (which I assume would go in parse.y), so I'd appreciate the help of someone who's familiar with the intricacies of parse.y.
Best,
William Woodruff
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
What about
MY_HASH = Hash.new {|h, k| "other value"}.update(
key: "value",
).freeze
?
Updated by woodruffw (William Woodruff) over 7 years ago
Nobuyoshi Nakada wrote:
What about
MY_HASH = Hash.new {|h, k| "other value"}.update( key: "value", ).freeze
?
Ah, I forgot about that...
That definitely works, and solves the problem without a need for new syntax. Please close if you don't see the need for these changes.
Thanks!
Updated by woodruffw (William Woodruff) over 7 years ago
Realized I forgot commas in the examples:
my_hash = {
key: "value",
*: proc { |h, k| h[k] = "other value" },
}
and
my_hash = {
"key" => "value",
* => proc { |h, k| h[k] = "other value" },
}
Updated by nobu (Nobuyoshi Nakada) about 7 years ago
Maybe both of elements and a block would be nice.
Updated by matz (Yukihiro Matsumoto) about 7 years ago
- Status changed from Open to Rejected
I don't think default_proc
is not worth adding a new syntax.
Matz.
Updated by hsbt (Hiroshi SHIBATA) over 2 years ago
- Project changed from 14 to Ruby master