Rails 4.x and earlier didn't support `Mime::Type[:FOO]`, so libraries
that support multiple Rails versions would've had to feature-detect
whether to use `Mime::Type[:FOO]` or `Mime::FOO`.

`Mime[:foo]` has been around for ages to look up registered MIME types
by symbol / extension, though, so libraries and plugins can safely
switch to that without breaking backward- or forward-compatibility.

Note: `Mime::ALL` isn't a real MIME type and isn't registered for lookup
by type or extension, so it's not available as `Mime[:all]`. We use it
internally as a wildcard for `respond_to` negotiation. If you use this
internal constant, continue to reference it with `Mime::ALL`.

Ref. efc6dd55

This class gives us the `all?` predicate method that returns true
without hitting method missing

We don't want to manage a list of constants on `Mime::`.  Managing
constants is strange because it will break method caches, not to mention
looking up by a constant could cause troubles.  For example suppose
there is a top level constant `HTML`, but nobody registers the HTML mime
type and someone accesses `Mime::HTML`.  Instead of getting an error
about how the mime type doesn't exist, instead you'll get the top level
constant.

So, instead of directly accessing the constants, change this:

  Mime::HTML

To this:

  Mime::Type[:HTML]

http://msdn.microsoft.com/en-us/library/ms775147%28v=vs.85%29.aspx#_replace

Signed-off-by: NYehuda Katz <wycats@gmail.com>

[#536 state:resolved]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6744 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6470 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6159 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5912 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5695 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

respond_to recognizes JSON. render :json => @person.to_json automatically sets the content type and takes a :callback option to specify a client-side function to call using the rendered JSON as an argument. References #4185.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5694 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

Added the option for extension aliases to mime type registration [DHH] Refactored default mime types to use the extension framework instead of just declaring themselves verbosely

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5663 5ecf4fe2-1ee6-0310-87b1-e25e094e27de