[RCR] #inject, #partition expand array if arity > 2

ruby-talk
1

Moin!

Simon Strandgaard wrote:

It would be awesome, if #inject could do splitting when arity > 2.
For instance converting an array of pairs into a hash (arity==3):

x=[[“name”, “john”], [“age”, 20]]
p x.inject({}){|h,k,v|h[k]=v;h}
#=> {“name”=>“john”, “age”=>20}

This is already possible with a built-in ruby feature:

x=[[“name”, “john”], [“age”, 20]]
x.inject({}) { |h, (k,v)| h[k]=v; h } # => {“name”=>“john”, “age”=>20}

Regards,
Florian Gross

2

Florian Gross wrote:

Moin!
This is already possible with a built-in ruby feature:

x=[[“name”, “john”], [“age”, 20]]
x.inject({}) { |h, (k,v)| h[k]=v; h } # => {“name”=>“john”, “age”=>20}

I’ve not seen that syntax/semantics before. Is the |(k,v)| syntax documented somewhere?

I’m guessing it’s not in Pickaxe, since inject didn’t appear until later … or is this kind of syntax generally available when iterating over hashes (or anything with key/value pairs)?

It seems incredibly useful!

Cheers,

Harry O.

3

I believe it’s just assignment semantics.

Block parameters are set in the same way that an assignment statement is
evaluated, so essentially, it’s the same as something like:

x = [[“name”, “john”], [“age”, 20]]

h, (k,v) = {}, x[0]

which does:
h = {}
(k,v) = [“name”, “john”] # (k = “name”, v = “john”)

When assignments involve commas, they’re implicitly converted to arrays, so
the above is the same as:

[h, [k, v]] = [{}, x[0]]

which explains why things happen the way they do.

Cheers,

  • Dan