Implement modular compilation

test/samples/funwithtypes.dart

-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// Some examples of how the dart type system/checked mode interacts with dart type unsoundness.
-// Suppose we were to "trust types" in the following sense: if the program passes the dart
-// type checker, assume that all checks implied by checked mode would have passed, and
-// compile under that assumption.  What does that buy you?  These examples are intended to
-// illustrate why this is less than you might think.  This file has no static errors or
-// warnings, and runs fine in checked mode, but it demonstrates lots of ways in which
-// nonetheless we can produce no such method errors, or sideways casts, etc.
-
-// A simple class
-class A {
-  int x = 0;
-}
-
-// Overriding x with an assignable type (supertype) is ok
-class B extends A {
-  num x = 1.0;
-  int y = 1;
-}
-
-// Contain a B
-class S0 {
-  B field;
-}
-
-// Override to an A
-class S1 extends S0 {
-  A field;
-  S1(A this.field);
-}
-
-// If we assume that s has type S0, can we assume that s.field has type B? No.
-void nsm0(S0 s) {
-  // Dynamic dispatch required.
-  // With global subclass information, the compiler could potentially get rid
-  // of some of the checks here when bad overrides as above don't happen.
-  try {
-    s.field.y;
-  } on NoSuchMethodError catch (r) {
-    print("Oops, no field y in something of type B");
-  }
-}
-
-// If we assume that f returns a B, can we assume that B.y exists? No.
-void nsm1(B f()) {
-  // Dynamic dispatch required.
-  // Even with global subclass info, the compiler can't do anything here, since
-  // this relies on screwy subtyping rather than screwy field overrides.
-  try {
-    f().y;
-  } on NoSuchMethodError catch (r) {
-    print("Oops, no field y in something of type B (extra badness)");
-  }
-}
-
-// If we assume that s is an S1, can we assume that s.field is an A? No.
-void doubleForInt0(S1 s) {
-  // Dynamic dispatch required.
-  // With global subclass info we can possibly know when we need to emit careful code
-  // here, but we certainly can't just generate a simple unconditional primitive operation
-  // (even ignoring nulls)
-  s.field.x + 1;
-  if (s.field.x is double) {
-    print("Oops, got double for int");
-  }
-}
-
-// Can we assume that f returns an int (or a subtype of an int)? No.
-// Can we assume that f returns an int (or subtype or a supertype of an int)? No.
-void doubleForInt1(int f()) {
-  // Dynamic dispatch required.
-  // Here, even with global subclass info we're still stuck - we can't really
-  // ever trust the return types on closures.  Note that int and double aren't
-  // even assignment compatible in this case.
-  f() + 1;
-  if (f() is double) {
-    print("Oops, got double for int (extra badness)");
-  }
-}
-
-class C extends A {}
-
-// Can we assume that f returns something on the same branch of the inheritance chain as B? No.
-void sidewaysCast(B f()) {
-  // Just to emphasize the point, here's a more general case where the static type
-  // isn't even on the same branch of the subtype hierarchy as the dynamic type.
-  if (f() is C) {
-    print(
-        "Static type of expression is B, but runtime type is C (neither sub nor supertype)");
-  }
-  if (f() is B) {
-    // Do something here.  This code doesn't get reached.... unless the compiler optimizes
-    // based on trusting types and  eliminates the is check, in which case we may suddenly
-    // execute different code.
-  }
-}
-
-// If we assume that x has type List<B>, what can we assume about the type of the elements?  Nothing.
-void generic0(List<B> x) {
-  // What can we assume about the elements of this array if we trust types?
-  // Absolutely nothing, whatsoever.
-  if (x[0] is int) {
-    print(
-        "Parameter type is List<B> but actually contains an int (completely unrelated type)");
-  }
-}
-
-void main() {
-  nsm0(new S1(new A()));
-  nsm1(() => new A());
-  doubleForInt0(new S1(new B()));
-  doubleForInt1(() {
-    num b = 1.0;
-    return b;
-  });
-  sidewaysCast(() {
-    A a = new C();
-    return a;
-  });
-  generic0(<dynamic>[3]);
-}