# method_missing

The Method gem you’ve been waiting for.

The method_missing gem brings the functional tools you need to Ruby: method composition, sequencing, and repeating. These are useful for when you must combine methods, apply different methods to the same argument, or “grow” a method.

I’ll explain, but first:

## Installing

```
gem install method_missing
```

## Usage: Composing

This is the classic. In algebra class you learned that `f(g(x))`

can also be written `(f . g)(x)`

. This is handy because now you have this `(f . g)`

object that you can pass to integrals and whatnot.

So in Ruby, using the method_missing gem:

```
def escape_everything(text)
everything_ecaper.call(text)
end
def everything_ecaper
method(:html_escape) * method(:escape_javascript) * method(:json_escape)
end
```

And more algebraically:

```
(f * g).call(x) == f.call(g.call(x))
```

## Usage: Sequencing

This doesn’t come up as often but when it does, oh boy, does it ever! This is useful for when you have a bunch of methods to apply to the same argument. For example, using the method_missing gem:

```
def (, )
.at_most_one(
(method(:sort_mod_time) / method(:sort_access_time)).call()) &&
.at_most_one(
(method(:sort_file_size) / method(:sort_mod_time)).call())
end
```

Again, more algebraically:

```
(f / g / h).call(x) == [f.call(x), g.call(x), h.call(x)]
```

## Usage: Repeating

This one comes up the least in most people’s day-to-day life. It’s the concept of applying a method to its output, repeatedly. Here’s a contrived example, using the method_missing gem:

```
def church_encoding(n)
if n.zero?
lambda{|f,x| x}
else
lambda{|f,x| (f ^ n).call(x)}
end
end
```

Algebraically:

```
(f ^ 3).call(4) == f.call(f.call(f.call(4)))
```

## Usage: Combining

These are objects which can be combined! Here’s an example, also contrived, that turns an object into a number, *n*, then adds four to *n* and multiplies *n* by six, then sums those results, using primitive methods that add one to a number and multiply a number by two:

```
def interesting_math(o)
four_and_six.call(o).sum
end
def four_and_six
((add1 ^ 4) / (mul2 ^ 3)) * method(:to_i)
end
```

To show this algebraically:

```
(((add1 ^ 4) / (mul2 ^ 3)) * method(:to_i)).call(o) == [
add1.call(add1.call(add1.call(add1.call(o.to_i)))),
mul2.call(mul2.call(mul2.call(o.to_i)))
]
```

## Copyright

Copyright 2011 Mike Burns