Default initial value of var fields of struct type (both backends)

I believe you are talking about v3/nbody.x10.
Actually, Body.sun() does not initialize p and v fields, NPE should happen.
Or am I missing something?

Oops. Yes, this is v3. Attaching the x10 source file, as intended

Oh good catch. I didn't realize that. So I guess the NPE is correct. So there are two problems here:
1) The Java backend needs to give an X10 stack trace (there's another JIRA open for this.)
2) This must be a bug with the C++ backend, since the C++ backend does NOT give an NPE:

dyn9002042056:tmp sjfink$ ~/work/x10-trunk/x10.dist/bin/x10c++ -o nbody nbody.x10
dyn9002042056:tmp sjfink$ ~/work/x10-trunk/x10.dist/bin/runx10 nbody 1
-0.169075164
-0.169074954

The NPE is not correct. vector is a struct.

So one of two things should have happened (depending on the semantics of default values).
(a) the typechecker should have rejected the program.
(b) the Java backend needs to support default initialization of structs that (recursively) contain only types that have zero as a legal default value.

I think (b) is what probably should be fixed. The C++ backend is doing this (easy for C++ since structs are inline, therefore initialiaizing a field of struct type that is zero-initialized is just as easy as initializing a field of a built-in primitive type that is zero-initialized.

Note that one possible fix for this would be for the front-end to explicitly insert assignments to default values to uninitialized field in the constructor.

Where can I find the definition of default value for each type? I cannot find it in the latest language spec document.

I suspect it isn't written in the spec.

The default value of a primitive struct type (int, float, etc) is the appropriate number of bytes of zeros. Default value of an Object is null. Apply inductively to structs. So something like:

struct A {
  a:int;
  b:int;
}

class C {
  var a:A;
}

new C().a.a  will result in 0, not a NPE.  

Is this true even if a type has default constructor that initializes some fields with non-zero value?

Yoav, can you provide a definitive answer.

We think that something like:

struct S {
  x:int = 4;
  y:int;
}

class C {
  var s:S
}

new C().s.x // equals 4
new C().s.y // equals 0

C++ backend compiles the above example as zero for both x and y. I think this is a front-end issue which should generate default constructor call at AST level. We need the specification anyway.

The front-end doesn't allow default value for user-defined structs.

We allow default values for:

• a type that can be null (e.g., Any, closures, but not a struct or Any {self!=null}

  )

• primitive/basic structs (user defined structs do not have a default).
  // includes: Int, Long, ULong, UInt, Float, Double, Boolean, Char
  // excludes: Short,UShort,Byte,UByte (because we do not have a literal of that type, there is a jira opened for Charles)

So the following code gives a fron-end error:

struct S {
  val x:int = 4;
  val y:int = 0;
}

class C {
  var s:S; // ERR: Field 's' was not definitely assigned.
}

This will solve the problem in the java backend (it will be complicated to do the 0-initialization on the java backend cause the user might already have defined a empty ctor that doesn't do 0-initialization).

bulk close of 2.1.0 resolved issues.