Ruby: map an array of keys to values shorthand

Question

I just started with Ruby recently and I'm hoping there is a shorthand for using a bound method as a proc I'm missing. I'm trying to do this essentially

SYMBOLS = {"I" => 1, "V" => 5, "X" => 10, ... }

roman = "zXXIV".upcase.chars.collect { |c| SYMBOLS[c] }
=> [nil, 10, 10, 1, 5]

I feel like there should be an easy way in ruby to just use SYMBOLS[] as a bound method, so just

roman = str.upcase.chars.collect &:SYMBOLS[]

Solution Ruby 1.9.3

roman = SYMBOLS.values_at(*str.upcase.chars)

Answer 1

SYMBOLS.values_at(str.upcase.chars.to_a)

Regarding using SYMBOLS[], you'd still need to pass the character to the method.

You can get the method via SYMBOLS.method(:[]), e.g.,

> p = SYMBOLS.method(:[])
> p.call("X")
=> 10

I'm not convinced it's the most readable in this case–for me, calling map and passing in SYMBOLS[], while concise and functional, delays understanding what's happening longer than I prefer.

Answer 2

SYMBOLS = {"I" => 1, "V" => 5, "X" => 10 }
roman = "zXXIV"

p roman.chars.map(&SYMBOLS.method(:[]))
#=> [nil, 10, 10, 1, 5]