Ranges

Ranges of numbers: a..b and a..>b.

a..b (half-open) holds a up to but not including b; a..>b (closed) includes b. Both make a Range<T>, a value that a for loop steps through without allocating:

for (var i in 0..count) { ... }   # 0, 1, ..., count - 1
for (var i in 1..>10) { ... }     # 1, 2, ..., 10

Source: runtime/range.pep

Range

[Value] struct Range<T>

A run of consecutive numbers, from start up to end, as a..b and a..>b make it.

A range is an iterator: next() steps from start up by one, and a for loop over a range is a counting loop. A range whose start is past its end yields nothing. A closed range ending at the largest value of its type (0..>255 as byte) stops there without overflowing.

Ranges are value structs: copying one copies its position, and looping over a range stored in a variable advances that variable.

Type parameters

• T — the number type, inferred from the bounds (0..n with a ulong n is a Range<ulong>)

Example

var total = 0;
for (var i in 1..>4) {
    total += i;   # 1 + 2 + 3 + 4
}
var r = 0..10;
assert(r.contains(9) && !r.contains(10), "half-open");

Fields

start

T start

The first number of the range.

end

T end

The bound the range stops at: the last number when inclusive, else one past it.

inclusive

bool inclusive

Whether end is part of the range: true for a..>b, false for a..b.

Properties

is_empty

var is_empty: bool { get; }

Whether the range holds no numbers, whatever the iteration has reached.

Constructor

Range()

construct(start: T, end: T, inclusive: bool = false)

Makes the range from start to end, as start..end (or start..>end when inclusive).

Parameters

• start — the first number
• end — the bound: one past the last number, or the last number when inclusive
• inclusive — whether end is part of the range

Methods

next

next(): bool

Advances to the next number: start on the first call, then one more each time.

Once it returns false it keeps returning false.

Returns

• true if there is a current number, false once past the end

current

current(): T

Returns the number the last successful next() moved to.

Returns

• the current number

Panics

• if next() was never called (“Range.current() before next()”)
• if next() already returned false (“Range.current() past the end”)

contains

contains(value: T): bool

Returns whether value lies in the range, whatever the iteration has reached.

Parameters

• value — the number to test

Returns

• true if start <= value and value is before end (or equal to it, for a closed range)