The gem dependencies platform is different from Gem::Platform. A platform gem.deps.rb platform matches on the ruby engine, the ruby version and whether or not windows is allowed.

:ruby, :ruby_XY: Matches non-windows, non-jruby implementations where X and Y can be used to match releases in the 1.8, 1.9, 2.0 or 2.1 series.
:mri, :mri_XY: Matches non-windows C Ruby (Matz Ruby) or only the 1.8, 1.9, 2.0 or 2.1 series.
:mingw, :mingw_XY: Matches 32 bit C Ruby on MinGW or only the 1.8, 1.9, 2.0 or 2.1 series.
:x64_mingw, :x64_mingw_XY: Matches 64 bit C Ruby on MinGW or only the 1.8, 1.9, 2.0 or 2.1 series.
:mswin, :mswin_XY: Matches 32 bit C Ruby on Microsoft Windows or only the 1.8, 1.9, 2.0 or 2.1 series.
:mswin64, :mswin64_XY: Matches 64 bit C Ruby on Microsoft Windows or only the 1.8, 1.9, 2.0 or 2.1 series.
:jruby, :jruby_XY: Matches JRuby or JRuby in 1.8 or 1.9 mode.
:maglev: Matches Maglev
:rbx: Matches non-windows Rubinius

NOTE: There is inconsistency in what environment a platform matches. You may need to read the source to know the exact details.

Gem::RequestSet::GemDependencyAPI#platforms

Block form for restricting gems to a particular set of platforms. See platform.

Gem::RequestSet::Lockfile#to_s

The contents of the lock file.

Gem::Resolver::ActivationRequest#to_s

No documentation available

Gem::Resolver::ActivationRequest#installed?

True if the requested gem has already been installed.

Gem::Resolver::ActivationRequest#parent

Return the ActivationRequest that contained the dependency that we were activated for.

Gem::Resolver::APISet#prefetch

A hint run by the resolver to allow the Set to fetch data for DependencyRequests reqs.

Gem::Resolver::ComposedSet#remote=

Sets the remote network access for all composed sets.