18.1 Assignment

Once you have a pointer to an object, you may be able to modify it. If the object type is first class, or otherwise assignable, you can put a new value into the object:

  begin
    var x: int = 0;       // make an object 
    val px = &x;          // find its address
    px <- 1;              // store new value at pointer
    println$ x;           // 1 : the object has been set to a new value
  end

Using the heap:

  begin
    val px = unbox (new 0);
    px <- 1;
    println$ *px;
  end

The store operator {<-} has the type:

    &T * T -> void

Felix also provides the more traditional assignment operator {=}:

  begin
    var x = 1; 
    x = 2;       // syntactic sugar for &x <- 2
    println$ x;  // 2
  end

but as you can see it is just syntactic sugar. All mutators work this way for example:

  begin
    var x = 1;
    x++;    // syntactic sugar for post_dec (&x)
    x+=1;   // syntactic sugar for plus_eq (&x,1)
  end

In particular all operators and functions except {&} accept values: there are no reference types. There are no operations which modify values directly.

Some values, when encoded in object store, can be modified partially via a pointer to that store. Clearly scalar values cannot be partially modified, most aggregates can be.

For Felix types, whether or not this is possible is determined solely by functions that manipulate pointers to objects storing those values.

For types defined in C++ and lifted into Felix, the programmer may provide mutators.