% composer require symfony/symfony ^3.0
./composer.json has been created
Loading composer repositories with package information
Updating dependencies (including require-dev)
  - Installing psr/log (1.0.0)
    Loading from cache

  - Installing doctrine/lexer (v1.0.1)
    Loading from cache

  - Installing doctrine/inflector (v1.1.0)
    Loading from cache

  - Installing doctrine/collections (v1.3.0)
    Loading from cache

  - Installing doctrine/cache (v1.6.0)
    Loading from cache

  - Installing doctrine/annotations (v1.2.7)
    Loading from cache

  - Installing doctrine/common (v2.6.1)
    Loading from cache

  - Installing psr/cache (1.0.1)
    Loading from cache

  - Installing twig/twig (v1.24.1)
    Loading from cache

  - Installing symfony/polyfill-util (v1.2.0)
    Loading from cache

  - Installing paragonie/random_compat (v2.0.2)
    Loading from cache

  - Installing symfony/polyfill-php70 (v1.2.0)
    Loading from cache

  - Installing symfony/polyfill-php56 (v1.2.0)
    Loading from cache

  - Installing symfony/polyfill-mbstring (v1.2.0)
    Loading from cache

  - Installing symfony/polyfill-intl-icu (v1.2.0)
    Loading from cache

  - Installing symfony/symfony (v3.1.3)
    Loading from cache

paragonie/random_compat suggests installing ext-libsodium (Provides a modern crypto API that can be used to generate random bytes.)
symfony/polyfill-intl-icu suggests installing ext-intl (For best performance)
Writing lock file
Generating autoload files

 % composer require cache/psr-6-doctrine-bridge
Using version ^2.2 for cache/psr-6-doctrine-bridge
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for cache/psr-6-doctrine-bridge ^2.2 -> satisfiable by cache/psr-6-doctrine-bridge[2.2.0].
    - cache/psr-6-doctrine-bridge 2.2.0 requires psr/cache-implementation ^1.0 -> no matching package found.

Potential causes:
 - A typo in the package name
 - The package is not available in a stable-enough version according to your minimum-stability setting
   see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details.

Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.

Installation failed, reverting ./composer.json to its original content.

 % composer require symfony/cache cache/psr-6-doctrine-bridge
Using version ^3.1 for symfony/cache
Using version ^2.2 for cache/psr-6-doctrine-bridge
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
  - Removing symfony/symfony (v3.1.3)
  - Installing symfony/symfony (v3.0.9)
    Loading from cache

  - Installing symfony/cache (v3.1.3)
    Loading from cache

  - Installing cache/psr-6-doctrine-bridge (2.2.0)
    Loading from cache

symfony/cache suggests installing symfony/polyfill-apcu (For using ApcuAdapter on HHVM)
Writing lock file
Generating autoload files