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+ 6.1 Pointers

We have introduced variables of the var kind, and now for the dreaded pointers! Again, our standard bindings: 

  include "./intro_02";


hello world
3
mytrue
3
2

and now we meet pointer types: 

  var x : myint = one;
  var px : &myint = &x;
  myprintln (*px);


1

+ 6.1.1 Address of operator &

The address-of operator {&} can be used to take the address of a variable of some type T to produce a value of type pointer-to-T, written {&T}.

In the example, we have a variable x of type myint and we take its address and put it in another variable px of type {&myint}.

+ 6.1.2 Dereference operator *

We can use the dereference operator {*} on any value of type {&T} to fetch a value of type T from the storage location pointer at by the ponter. In the example, we retrieve the value of type myint from the pointer px of type {&myint) this way.

This is not particularly useful, however if we assign a new value to x we retrieve that too: 

  x = two;
  myprintln (*px);


2

+ 6.1.3 Assignment through pointer <-

We can also assign a value to the store pointed at by px through that pointer: 

  px <- two;
  myprintln (x);


2

From these rules you may understand that var-ables are addressable and mutable. The store a var-able represents is one example of an object which may hold a value, however which value may change with time.

The distinction between objects and values is crucial: in Felix all values are immutable and cannot be modified.