For Loop
Iterating through a numeric range or an array, or any type with a registered type iterator,
is provided by the for
… in
loop.
There are two alternative syntaxes, one including a counter variable:
for
variablein
expression{
…}
for (
variable,
counter)
in
expression{
…}
`for` loops can be disabled via [`Engine::set_allow_looping`][options].
Counter Variable
The counter variable, if specified, starts from zero, incrementing upwards.
let a = [42, 123, 999, 0, true, "hello", "world!", 987.6543];
// Loop through the array
for (item, count) in a {
if x.type_of() == "string" {
continue; // skip to the next iteration
}
// 'item' contains a copy of each element during each iteration
// 'count' increments (starting from zero) for each iteration
print(`Item #${count + 1} = ${item}`);
if x == 42 { break; } // break out of for loop
}
Break or Continue
Like C, continue
can be used to skip to the next iteration, by-passing all following statements;
break
can be used to break out of the loop unconditionally.
Iterate Through Arrays
Iterating through an array yields cloned copies of each element.
let a = [1, 3, 5, 7, 9, 42];
// Loop through the array
for x in a {
if x > 10 { continue; } // skip to the next iteration
print(x);
if x == 42 { break; } // break out of for loop
}
Iterate Through Strings
Iterating through a string yields individual characters.
The chars
method also allow iterating through characters in a string, optionally accepting the
character position to start from (counting from the end if negative), as well as the number of
characters to iterate (defaults to all).
char
also accepts a range which can be created via the ..
(exclusive) and ..=
(inclusive) operators.
let s = "hello, world!";
// Iterate through all the characters.
for ch in s {
print(ch);
}
// Iterate starting from the 3rd character and stopping at the 7th.
for ch in s.chars(2, 5) {
if ch > 'z' { continue; } // skip to the next iteration
print(ch);
if x == '@' { break; } // break out of for loop
}
// Iterate starting from the 3rd character and stopping at the end.
for ch in s.chars(2..s.len) {
if ch > 'z' { continue; } // skip to the next iteration
print(ch);
if x == '@' { break; } // break out of for loop
}
Iterate Through Numeric Ranges
Ranges are created via the ..
(exclusive) and ..=
(inclusive) operators.
The range
function similarly creates exclusive ranges, plus allowing optional step values.
// Iterate starting from 0 and stopping at 49
// The step is assumed to be 1 when omitted for integers
for x in 0..50 {
if x > 10 { continue; } // skip to the next iteration
print(x);
if x == 42 { break; } // break out of for loop
}
// The 'range' function is just the same
for x in range(0, 50) {
if x > 10 { continue; } // skip to the next iteration
print(x);
if x == 42 { break; } // break out of for loop
}
// The 'range' function also takes a step
for x in range(0, 50, 3) { // step by 3
if x > 10 { continue; } // skip to the next iteration
print(x);
if x == 42 { break; } // break out of for loop
}
// The 'range' function can also step backwards
for x in range(50, 0, -3) { // step down by -3
if x < 10 { continue; } // skip to the next iteration
print(x);
if x == 42 { break; } // break out of for loop
}
// It works also for floating-point numbers
for x in range(5.0, 0.0, -2.0) { // step down by -2.0
if x < 10 { continue; } // skip to the next iteration
print(x);
if x == 4.2 { break; } // break out of for loop
}
Iterate Through Bit-Fields
The bits
function allows iterating through an integer as a bit-field.
bits
optionally accepts the bit number to start from (counting from the most-significant-bit if
negative), as well as the number of bits to iterate (defaults all).
bits
also accepts a range which can be created via the ..
(exclusive) and ..=
(inclusive) operators.
let x = 0b_1001110010_1101100010_1100010100;
let num_on = 0;
// Iterate through all the bits
for bit in x.bits() {
if bit { num_on += 1; }
}
print(`There are ${num_on} bits turned on!`);
const START = 3;
// Iterate through all the bits from 3 through 12
for (bit, index) in x.bits(START, 10) {
print(`Bit #${index} is ${if bit { "ON" } else { "OFF" }}!`);
if index >= 7 { break; } // break out of for loop
}
// Iterate through all the bits from 3 through 12
for (bit, index) in x.bits(3..=12) {
print(`Bit #${index} is ${if bit { "ON" } else { "OFF" }}!`);
if index >= 7 { break; } // break out of for loop
}
Iterate Through Object Maps
Two methods, keys
and values
, return arrays containing cloned copies
of all property names and values of an object map, respectively.
These arrays can be iterated.
let map = #{a:1, b:3, c:5, d:7, e:9};
// Property names are returned in unsorted, random order
for x in map.keys() {
if x > 10 { continue; } // skip to the next iteration
print(x);
if x == 42 { break; } // break out of for loop
}
// Property values are returned in unsorted, random order
for val in map.values() {
print(val);
}