Fuzion • Tutorial • Fields

Fields

So far, we have seen features that were implemented as routines. An alternative to implementing a feature as a routine is implementing it as a field.

Argument Fields

Let us start with a small example that declares a feature Point with two arguments x and y of type i32, which is a 32-bit signed integer value:

example is
{
  Point(x, y i32) is { }

  show(Point(3, 4));
  show(Point(5, 12));

  show(p Point) unit =>
  {
    say("{p.x}, {p.y}");
  }
}

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example is
{
  Point(x, y i32) is { }
  show(Point(3, 4));
  show(Point(5, 12));
  show(p Point) unit =>
  {
    say("{p.x}, {p.y}");
  }
}
 
 
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What are effects?

The arguments x and y are inner features of Point. Argument features are always fields. Fields can store a value, they are similar to function features without arguments and a pre-determined result value.

The example creates two instances of Point with values Point 3 4 and Point 5 12 and passes these to routine show. show then calls Point.x and Point.y on its argument p to print the point's coordinates.

Non-Argument Inner Fields

Fields can also be declared in the code section of a routine. The following example declares two fields p1 and p2 of type Point. As part of the declaration, instances of Point with values Point 3 4 and Point 5 12 are created. These points are assigned to p1 and p2 using the assignment operator :=.

Like before, these points are passed to a routine show, but this time they are read from fields p1 and p2.

example is
{
  Point(x, y i32) is { }

  p1 Point := Point(3, 4);
  p2 Point := Point(5, 12);

  show(p1);
  show(p2);

  show(p Point) unit =>
  {
    say("{p.x}, {p.y}");
  }
}

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example is
{
  Point(x, y i32) is { }
  p1 Point := Point(3, 4);
  p2 Point := Point(5, 12);
  show(p1);
  show(p2);
  show(p Point) unit =>
  {
    say("{p.x}, {p.y}");
  }
}
 
 
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What are effects?

Type Inference for Fields

Similar to the result type inference of function features, a field's type can be inferred automatically from the value assigned to it, the type in the declaration of p1 and p2 in this example can be omitted:

example is
{
  Point(x, y i32) is { }

  p1 := Point(3, 4);
  p2 := Point(5, 12);

  show(p1);
  show(p2);

  show(p Point) unit =>
  {
    say("{p.x}, {p.y}")
  }
}

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example is
{
  Point(x, y i32) is { }
  p1 := Point(3, 4);
  p2 := Point(5, 12);
  show(p1);
  show(p2);
  show(p Point) unit =>
  {
    say("{p.x}, {p.y}")
  }
}
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

Type Inference for Argument Fields

Fuzion can in some cases even infer the types of a feature's argument fields. That way, feature declarations will look similar to implementations in a dynamically typed language like Python. In the example, we can omit the type in the declaration of Point and show:

example is
{
  Point(x, y) is { }

  p1 := Point(3, 4);
  p2 := Point(5, 12);

  show(p1);
  show(p2);

  show(p) unit =>
  {
    say("{p.x}, {p.y}")
  }
}

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example is
{
  Point(x, y) is { }
  p1 := Point(3, 4);
  p2 := Point(5, 12);
  show(p1);
  show(p2);
  show(p) unit =>
  {
    say("{p.x}, {p.y}")
  }
}
 
 
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What are effects?

Repeated Field Declarations

Field shadowing sometimes called variable shadowing is not allowed in fuzion.

last changed: 2024-08-13

next: Empty Constructors