How do I pass a lambda to Hash.each?

Question

How can I pass a lambda to `hash.each`, so I can re-use some code? ``` > h = { a: 'b' } > h.each do |key, value| end => {:a=>"b"} > test = lambda do |key, value| puts "#{key} = #{value}" end > test.call('a','b') a = b > h.each &test ArgumentError: wrong number of arguments (1 for 2) from (irb):1:in `block in irb_binding' from (irb):5:in `each' from (irb):5 from /Users/jstillwell/.rvm/rubies/ruby-1.9.3-p362/bin/irb:16:in `

' > h.each test ArgumentError: wrong number of arguments(1 for 0) from (irb):8:in `each' from (irb):8 from /Users/jstillwell/.rvm/rubies/ruby-1.9.3-p362/bin/irb:16:in `

' ```

Accepted Answer

`each` yields the current element to the block, ergo the lambda needs to take one argument, not two. In case of a `Hash` the element being yielded is a two-element `Array` with the first element being the key and the second element being the value.

```
test = lambda do |el| puts "#{el.first} = #{el.last}" end
h.each &test
# a = b
```

Alternatively, you can use Ruby's support for destructuring bind in parameter lists:

```
test = lambda do |(k, v)| puts "#{k} = #{v}" end
h.each &test
# a = b
```

Or, instead of using a `lambda` which has the same argument binding semantics as a method, you could use a `Proc`, which has the same argument binding semantics as a block, i.e. it will unpack a single `Array` argument into multiple parameter bindings:

```
test = proc do |k, v| puts "#{k} = #{v}" end
h.each &test
# a = b
```

How do I pass a lambda to Hash.each?

Solution

Problem