Comparison of type systems

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Programming language static / dynamic strong / weak safety nominative / structural
Ada static strong safe nominative
Assembly language none strong unsafe structural
APL dynamic weak safe nominative
BASIC static weak safe nominative
C static weak unsafe nominative
C++ static strong unsafe nominative
C#[1] static strong both nominative
Cayenne dependent strong safe structural
Centura static weak safe nominative
Clipper dynamic weak safe duck
D static strong both[2] nominative
Delphi static strong safe nominative
E dynamic strong safe nominative + duck
Eiffel static strong safe nominative
Erlang dynamic strong safe nominative
Fortran static strong safe nominative
Go static strong safe structural
Groovy dynamic strong safe duck
Haskell static strong safe nominative
Io dynamic strong safe duck
Java static strong safe nominative
JavaScript dynamic weak safe duck
Lisp dynamic strong safe structural
Lua[3] dynamic weak safe structural
ML static strong safe structural
Objective-C[4] dynamic strong unsafe duck
Pascal static strong safe nominative
Perl 1-5 dynamic weak safe nominative
Perl 6[5] hybrid hybrid safe duck
PHP dynamic weak safe  ?
Pike static+dynamic strong safe structural
Python dynamic strong safe duck
Ruby dynamic strong safe duck
Scala[6] static strong safe structural
Scheme dynamic strong safe nominative
Smalltalk dynamic strong safe duck
Visual Basic hybrid hybrid safe nominative
Windows PowerShell hybrid hybrid safe duck
xHarbour dynamic weak safe duck
Ya static strong unsafe nominative
  1. ^ The C basis is unchanged. 3.0 has hybrid typing with Anonymous Types. Can be both unsafe and safe with use of 'unsafe' functions and code blocks.
  2. ^ D's philosophy is: safe by default with unsafe "backdoors". D also supports @safe functions that provably can't corrupt memory at the cost of disabling some of the unsafe language constructs.
  3. ^ Variables can change type with the use of metatables.
  4. ^ Applies to the Objective-C extension only.
  5. ^ Not yet released.
  6. ^ Scala supports structural types through runtime reflection on the JVM