Ranges

Current boundary:

• range expressions are not part of the current compiler surface; the compiler rejects them with a “not yet supported” diagnostic (T1002)
• range-based loop headers and range matching described in other chapters inherit this boundary and are not executable today
• everything below describes intended design, not current behavior
• this is later design work, not part of the current V1 compiler surface

There are two range expressions:

• Defined ranges
• Undefined ranges

Defined ranges

Defined ranges represent a group of values that are generated as a sequence based on some predefined rules. Ranges are represented with two dots .. operator.

{ 1..8 }                // a range from 1 to 8
{ 1,2,3,4,5,6,7,8 }

{ 8..1 }                // a range from 8 to 1
{ 8,7,6,5,4,3,2,1 }

{ 1..8..2 }             // a range from 1 to 8 jumping by 2
{ 1,3,5,7 }

{ 3..-3 }               // a range from 4 to -4
{ 3,2,1,0,-1,-2,-3 }

{ -3..3 }               // a range from -3 to 3
{ -3,-2,-1,0,1,2,3 }

{ ..5 }                 // a range form 0 to 5 
{ 0,1,2,3,4,5 }

{ ..-5 }                // a range from 0 to -5
{ 0,-1,-2,-3,-4,-5 }

{ 5.. }                 // a range from 5 to 0
{ 5,4,3,2,1,0 }

{ -5.. }                // a range from -5 to 0
{ -5,-4,-3,-2,-1,0 }

Undefined ranges

Undefined ranges represent values that have only one side defined at the definition time, and the compiler defines the other side at compile time. They are represented with three dots ...

{ 2... }                // from 2 to infinity

In most of the cases, they are used for variadic parameters passing:

fun calc(number: ...int): int = { return number[0] + number[1] + number[2] * number[3]}