1. if-(else)
   • General Form
   • Type Conversions and Assignments
   • Casting
   • Type Checking
2. switch-case
   • General Form

if-(else)

Use if-(else) statements to select a statement or block of code to execute based on a condition.

General Form

If-statements have the following general forms:

if (condition) consequence

if (condition) consequence
else alternative

if (condition0) consequence0
else if (condition1) consequence1
..
else if (conditionN) consequenceN
else alternative

where condition is a boolean expression and consequence and alternative are statements. The consequence is executed if condition is true. When several conditions exist with else if, the conditions are evaluated in order. When a condition is true and the corresponding consequence has been executed, processing stops. If no conditions are true, the alternative will be executed instead.

Type Conversions and Assignments

The condition can also contain type conversions and assignments like this:

id = expr

type id = expr

The consequence statement will only be executed if expr is not null, or has type bool and value true. The identifier id is only visible inside the consequence block, if it was declared inside the condition using the second form.

Casting

The condition can also contain type casting, using the keyword as, like this:

id as type

The consequence statement will only be executed if the casting of the identifier id into type was successful. Inside the consequence block, id is of type.

Example

{
    AShape2D shape = APolyline2D();
    
    // fillColor() is final in AShape2D and can be called directly.
    pln(shape.fillColor());
    
    if (shape as APolyline2D) {
        // count() extend APolyline2D and type casting is necessary.
        pln(#shape.count());
    }
}

Type Checking

The condition can also contain type checking (without casting), using the keyword in, like this:

id in type

The consequence statement will only be executed if id is of type. The initial typing of id will be maintained, even inside the consequence block.

Example

{
    AShape2D shape = APolyline2D();
    
    if (shape in APolyline2D) {
        pln("shape is a polyline!");
        //pln(#shape.count()); // Would give compile error
    }
}

See also: Type Tests and Conversions.

switch-case

Use switch statements to select a statement or block of code to execute based on comparison with a set of constant values. switch statements are a structured alternative to chains of if-else statements. They can help to detect programming mistakes such as repeated cases, and improve performance.

General Form

 switch(expr) {
     caseClause1
     caseClause2
     ..
     caseClausen
 }

where caseClause can have the forms

 case literal: stmt
 case literal1, literal2, .., literaln: stmt

 default: stmt

and literal is a literal of a supported type. No case may be repeated. The supported types are:

• all integer types except nat and int64
• all enum types
• integer ranges
• str
• symbol

The default case is chosen when the expression does not match any of the other cases. Failure to match an alternative will throw an exception if the default case was omitted.

Examples

{
    int x = 1;
    
    switch(x) {
      case 1: pln("one");
      case 2: pln("two");
      default: pln("other");
    }
}

{
    switch(x) {
      case 1, 3, 5: {
          pln("odd");
      }
        
      case 2, 4, 6: {
          pln("even");
      }
        
      default: pln("other");
    }
}

{
    switch(x) {
      case 0..9: pln("one digit");
      case 10..99: pln("two digits");
    }
}

{
    str s = getStr();
    
    switch(s) {
      case "SE": lang = "swedish";
      case "FR": lang = "french";
      default: ;
    }
}

{
    symbol sym;
    
    switch(sym) {
      case #"cm.core": pkg = "core";
      case #"cm.win": pkg = "win";
      default: pkg = "fail";
    }
}