feat($cacheFactory): Make Cache.put return the value

[taralx]

Using cache.put is slightly awkward because you can't just wrap an expression with it like you can a standard object.

Coffeescript with plain object:
cache = {}
(key) -> cache[key] ?= genValue(key)

Coffeescript with $cacheFactory cache:

cache = $cacheFactory.get('cache')
(key) -> cache.get(key) ? (r = genValue(key); cache.put(key, r); r)

With this change:

cache = $cacheFactory.get('cache')
(key) -> cache.get(key) ? cache.put(key, genValue(key))

[pkozlowski-opensource]

@taralx This looks good apart from the fact that the test could be simplified (let me know if I've missed anything).

Could you re-work the commit message as described in http://docs.angularjs.org/misc/contribute ?
You would also have to sign the CLA as well.

[taralx]

Updated.

[pkozlowski-opensource]

@taralx Did you sign the CLA?

[taralx]

Yes.

[IgorMinar]

this is useless because return undefined is the same thing as return.

[IgorMinar]

I was inclined to say no to this change because it looked like only coffee script would benefit from it, but it turns out that even in js you can simplify the code thanks to the ability to use ternary operators.

Before:

function getVal(key) {
  var val = cache.get(val);
  if (val === undefined) {
    val = getnerateVal(key);
    cache.put(key, val);
  }
  return val;
}

Before with inlined assignment:

function getVal(key) {
  var val = cache.get(val);
  if (val === undefined) {
    cache.put(key, val = getnerateVal(key));
  }
  return val;
}

After:

function getVal(key) {
  var val = cache.get(val);
  if (val === undefined) {
    val = cache.put(key, getnerateVal(key));
  }
  return val;
}

After w/ ternary operator:

function getVal(key) {
  var val = cache.get(val);
  return (val === undefined)
      ? cache.put(key, getnerateVal(key))
      : val;
}

[IgorMinar]

why not just var obj = {}, we just need to be able to test object identity and for that object literal is good enough.

[IgorMinar]

landed as 168db33

thanks!