Ranges
Syntax
Numeric ranges can be constructed by the .. (exclusive) or ..= (inclusive) operators.
Exclusive range
start
..end
An exclusive range does not include the last (i.e. “end”) value.
type_of() an exclusive range returns "range".
Inclusive range
start
..=end
An inclusive range includes the last (i.e. “end”) value.
type_of() an inclusive range returns "range=".
Usage Scenarios
Ranges are commonly used in the following scenarios.
| Scenario | Example |
|---|---|
for statements | for n in 0..100 { ... } |
in expressions | if n in 0..100 { ... } |
switch expressions | switch n { 0..100 => ... } |
| Bit-fields access | let x = n[2..6]; |
| Bits iteration | for bit in n.bits(2..=9) { ... } |
| Array range-based API’s | array.extract(2..8) |
| BLOB range-based API’s | blob.parse_le_int(4..8) |
| String range-based API’s | string.sub_string(4..=12) |
| Characters iteration | for ch in string.bits(4..=12) { ... } |
Built-in Functions
The following methods operate on ranges.
| Function | Parameter(s) | Description |
|---|---|---|
start method and property | beginning of the range | |
end method and property | end of the range | |
contains, in operator | number to check | does this range contain the specified number? |
is_inclusive method and property | is the range inclusive? | |
is_exclusive method and property | is the range exclusive? |
TL;DR
Rust has _open-ended_ ranges, such as `start..`, `..end` and `..=end`. They are not available in Rhai.
They are not needed because Rhai can overload functions.
Typically, an API accepting ranges as parameters would have equivalent versions that accept a
starting position and a length (the standard `start + len` pair), as well as a versions that accept
only the starting position (the length assuming to the end).
In fact, usually all versions redirect to a call to one single version.
Therefore, there should always be a function that can do what open-ended ranges are intended for.
The left-open form (i.e. `..end` and `..=end`) is trivially replaced by using zero as the starting
position with a length that corresponds to the end position (for `..end`).
The right-open form (i.e. `start..`) is trivially replaced by the version taking a single starting position.
~~~rust
let x = [1, 2, 3, 4, 5];
x.extract(0..3); // normal range argument
// copies 'x' from positions 0-2
x.extract(2); // copies 'x' from position 2 onwards
// equivalent to '2..'
x.extract(0, 2); // copies 'x' from beginning for 2 items
// equivalent to '..2'
~~~